So what does it mean when Christians end their prayers with the word Amen?
The word Amen is taken straight over from the Hebrew word without any translation. 

Amen means ‘may it be so in accordance with Your will.’
In essence, we are telling God that whatever our requests may be, our prayer’s primary principle is for it to be in accordance with God’s will alone.

Furthermore, when we say Amen, we are actually using the words of the creator himself.

The word Amen is a word that is identical with Jesus Christ as seen in the book of Revelation where He is the Amen, the faithful, the true witness, and the ruler of God’s creation so by using the word Amen we are also praying in the name of our Lord and Savior Jesus Christ.

Revelation 3:14 (NIV)

“To the angel of the church in Laodicea write: These are the words of the Amen, the faithful and true witness, the ruler of God’s creation.

2 Corinthians 1:20 (NIV)

For no matter how many promises God has made, they are “Yes” in Christ. And so through him, the “Amen” is spoken by us to the glory of God.