It's wonderful to see that you want to learn how to properly celebrate the festivals and Holy Days of the Bible. God's Word is very clear that these days are special to Him and that He expects His people to observe them. As shown in the booklet you mentioned, Jesus Christ kept the biblical Sabbath and Holy Days. The lead article of this issue, "Jesus Christ in the Biblical Festivals," shows how all of them teach us about Him and His role in God's great plan of salvation.
After His death and resurrection, the early Church continued to observe the weekly Sabbath and festivals of the Bible. Although specific details aren't given in every case, they had special worship services on these days since they are to be "holy convocations" (Leviticus 23:4 Leviticus 23:4These are the feasts of the LORD, even holy convocations, which you shall proclaim in their seasons.
American King James Version×).
A "holy convocation" is a sacred assembly that God has commanded. Today we conduct special services on the Holy Days, with sermons about the meaning and significance of the days, congregational hymns and Christian fellowship. Often several congregations will meet together in a central location.
As on the weekly Sabbath day, we do not do any of our customary work on the biblical Holy Days, as instructed in Leviticus 23.
The first of the annual biblical festivals listed after the weekly Sabbath in this chapter is the Passover, a memorial of the sacrifice of Jesus Christ for our sins, redeeming us from death. Accordingly, this period of the year is approached with deep spiritual introspection.
We commemorate the Passover on the evening of the 14th day of the first month of the sacred year (on the Hebrew calendar) with a service based on the apostle Paul's inspired instructions of 1 Corinthians 11:23-28 1 Corinthians 11:23-28  For I have received of the Lord that which also I delivered to you, That the Lord Jesus the same night in which he was betrayed took bread:
 And when he had given thanks, he broke it, and said, Take, eat: this is my body, which is broken for you: this do in remembrance of me.
 After the same manner also he took the cup, when he had supped, saying, This cup is the new testament in my blood: this do you, as oft as you drink it, in remembrance of me.
 For as often as you eat this bread, and drink this cup, you do show the Lord's death till he come.
 Why whoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord.
 But let a man examine himself, and so let him eat of that bread, and drink of that cup.
American King James Version×and the accounts in the four Gospels of the New Testament Passover that Christ instituted with His disciples.
This solemn evening service begins with a brief explanation of its purpose, followed by washing of one another's feet (based on Christ's example and instructions in John 13). Then the one conducting the service explains the symbols of the Passover—unleavened bread and wine—which represent the body and blood of our Savior. Each baptized member of the Church eats a small piece of the unleavened bread and drinks a small amount of wine, symbolizing that sacrifice on our behalf.
The Passover service is followed a day later by the beginning of the Feast of Unleavened Bread. This seven-day festival starts and ends with an annual Sabbath day on which church services are held similar to the kind of services we hold on every weekly Sabbath. However, on each of the annual Sabbaths during this feast and the other festivals, the messages focus on various aspects of the meaning of the day we are observing. The messages provide guidance, encouragement and education to the membership, as well as help us worship God.
(These annual Sabbaths or Holy Days are also times that freewill offerings are collected during services—God having told the Israelites to present offerings during the annual festival seasons, as stated in Deuteronomy 16:16-17 Deuteronomy 16:16-17  Three times in a year shall all your males appear before the LORD your God in the place which he shall choose; in the feast of unleavened bread, and in the feast of weeks, and in the feast of tabernacles: and they shall not appear before the LORD empty:
 Every man shall give as he is able, according to the blessing of the LORD your God which he has given you.
American King James Version×. Such offerings are not collected during weekly Sabbath services, though tithes and offerings can be sent in at any time.)
Specific to the Feast of Unleavened Bread is preparing for it by removing from our homes all leavening agents and leavened products (bread products made with yeast, sodium bicarbonate or baking powder)—leavening during this week symbolizing sin. We also do not eat bread products made with leaven during the Unleavened Bread festival in keeping with God's instructions (Exodus 12:15-20 Exodus 12:15-20  Seven days shall you eat unleavened bread; even the first day you shall put away leaven out of your houses: for whoever eats leavened bread from the first day until the seventh day, that soul shall be cut off from Israel.
 And in the first day there shall be an holy convocation, and in the seventh day there shall be an holy convocation to you; no manner of work shall be done in them, save that which every man must eat, that only may be done of you.
 And you shall observe the feast of unleavened bread; for in this selfsame day have I brought your armies out of the land of Egypt: therefore shall you observe this day in your generations by an ordinance for ever.
 In the first month, on the fourteenth day of the month at even, you shall eat unleavened bread, until the one and twentieth day of the month at even.
 Seven days shall there be no leaven found in your houses: for whoever eats that which is leavened, even that soul shall be cut off from the congregation of Israel, whether he be a stranger, or born in the land.
 You shall eat nothing leavened; in all your habitations shall you eat unleavened bread.
American King James Version×; 1 Corinthians 5:7-8 1 Corinthians 5:7-8  Purge out therefore the old leaven, that you may be a new lump, as you are unleavened. For even Christ our passover is sacrificed for us:  Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
American King James Version×). Instead we eat unleavened bread during this time. The spiritual picture is that we are to live a Christlike life by partaking of the true Bread of life—avoiding sin and taking in Christ's righteousness.
Two common commercial unleavened breads are Ry-Krisp and matzos (not all matzos products are leaven free, so one has to read the labels). Some members prefer to make their own unleavened bread to eat during this time.
As mentioned earlier, because the Holy Days are also Sabbaths, we are not to perform regular work on them, resting in the same way we do on every weekly Sabbath. (The Passover is a festival, but the Bible does not refer to it as a Sabbath. It is therefore permissible to work on Passover day following the memorial observance, particularly as it's a preparation time for the beginning of the Feast of Unleavened Bread.)
The evening that commences the Feast of Unleavened Bread is a special memorial of the Exodus from Egypt, picturing the deliverance from our past sinful lives, referred to as a "night to be much observed" (Exodus 12:42 Exodus 12:42It is a night to be much observed to the LORD for bringing them out from the land of Egypt: this is that night of the LORD to be observed of all the children of Israel in their generations.
American King James Version×, King James Version). Groups gather in homes or other places for a fellowship meal, often with a discussion of the significance of the evening.
The Day of Atonement has a unique aspect to it, in that God instructs us to afflict ourselves, which refers in other scriptures to fasting—going without food and drink on that day (Leviticus 23:27-29 Leviticus 23:27-29  Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation to you; and you shall afflict your souls, and offer an offering made by fire to the LORD.
 And you shall do no work in that same day: for it is a day of atonement, to make an atonement for you before the LORD your God.
 For whatever soul it be that shall not be afflicted in that same day, he shall be cut off from among his people.
American King James Version×; Isaiah 58:3 Isaiah 58:3Why have we fasted, say they, and you see not? why have we afflicted our soul, and you take no knowledge? Behold, in the day of your fast you find pleasure, and exact all your labors.
American King James Version×, Isaiah 58:5 Isaiah 58:5Is it such a fast that I have chosen? a day for a man to afflict his soul? is it to bow down his head as a bulrush, and to spread sackcloth and ashes under him? will you call this a fast, and an acceptable day to the LORD?
American King James Version×; Acts 27:9 Acts 27:9Now when much time was spent, and when sailing was now dangerous, because the fast was now already past, Paul admonished them,
American King James Version×). Children and those with medical conditions for whom fasting could be detrimental to their health are not expected to fast in this way.
Most of the Holy Days are observed in local congregations or in a gathering of several local congregations, with the exception of the seven-day Feast of Tabernacles and the Eighth Day immediately following. Members and their families gather in centralized locations throughout the United States and around the world for the entire eight-day period. We observe this main festival season of the year with church services on each of the eight days along with the opportunity for fellowship and recreation outside of services.
This festival, foreshadowing the coming reign of Jesus Christ on earth, is to be a time of great spiritual and physical enjoyment for everyone (Deuteronomy 14:26 Deuteronomy 14:26And you shall bestow that money for whatever your soul lusts after, for oxen, or for sheep, or for wine, or for strong drink, or for whatever your soul desires: and you shall eat there before the LORD your God, and you shall rejoice, you, and your household,
American King James Version×), so sharing meals and having fun with fellow church members at area attractions is encouraged. And our celebration includes programs and activities for families, seniors, teens and young adults.
If you would like to find information on meeting with others on the weekly Sabbath and annual Holy Days, please contact our minister in your area. You can find his name and phone number at ucg.org/churches. We think you will find it encouraging and refreshing to meet with others at these holy times God has given us.
For others desiring a detailed explanation of the biblical festivals and why we keep them, we encourage you to read our study guide God's Holy Day Plan: The Promise of Hope for All Mankind. We also publish a list of the dates for the Holy Days inside this study guide.