Our word amen comes from a Hebrew word that has a similar pronunciation. Strong's Concordance defines the word as "verily, truly, amen, or so be it." Saying "amen" at the end of a prayer states our affirmation that what was just said is true and that we are in agreement with the prayer.
In addition, the Bible uses the word Amen as one of the names of Jesus Christ. In Revelation 3:14 Revelation 3:14And to the angel of the church of the Laodiceans write; These things said the Amen, the faithful and true witness, the beginning of the creation of God;
American King James Version×, the message to the church in Laodicea calls Jesus the "Amen." Its use here connects His name with truth and emphasizes that what is said in this message is true.
Jesus gave His disciples a model for prayer in Matthew 6:9-13 Matthew 6:9-13  After this manner therefore pray you: Our Father which are in heaven, Hallowed be your name.
 Your kingdom come, Your will be done in earth, as it is in heaven.
 Give us this day our daily bread.
 And forgive us our debts, as we forgive our debtors.
 And lead us not into temptation, but deliver us from evil: For your is the kingdom, and the power, and the glory, for ever. Amen.
American King James Version×. In this sample prayer, Jesus set the example of ending it with "amen." Since Christians are instructed to follow the example and steps of Jesus (1 Peter 2:21 1 Peter 2:21For even hereunto were you called: because Christ also suffered for us, leaving us an example, that you should follow his steps:
American King James Version×), we close our prayers with "amen" just as He did.