Atheism is when someone does not believe in a god or gods. In Christianity, people believe in one god, who they call God. Some people choose to be atheists and do not believe in God, while others choose to believe in God and call themselves Christians.
In Christianity, some people believe that it is important to follow God's rules and teachings, and that doing so will lead to a happy and meaningful life. However, atheists do not believe that God exists, so they do not think it matters to follow His rules.
Some Christians may not like atheists because they do not believe in God, which goes against what Christianity teaches. But it is important to remember that everyone has the right to believe or not believe in whatever they want.