What do christians belevive happens after death?

Christians believe in life after death. Jesus Christ came to earth from heaven to pay the penalty for sin. When a person accepts Jesus Christ as their personal Savior they are given eternal life with Him in heaven. So when we died our soul goes to heaven to be with Jesus and our body remains on earth. At the coming time of the resurrection all Christians (bodies of Christians) will be raised up out of the graves and rejoined with their souls that God will bring with Him from heaven.

For the unsaved person when they die their body remains on earth and their soul goes to a temporary hell. When the time comes for the unsaved to be resurrected their soul will be rejoined to their body and they will stand in judgment before the Great White Throne. Their names will not be found in the Lamb's book of life and they will be sent to the Lake of Fire (Revelation 20:11-15) to suffer for eternity.

Please read The Bible as it explains all of this, as well as how you can come to Jesus Christ and be saved.