Salvation in Christianity means that you can go to heaven after you die. Heaven is a happy and peaceful place where people who did good things on Earth go when they die. But, to go to heaven, you must believe in God and Jesus, whom Christians believe is the son of God.
They also believe that Jesus died on the cross for our sins and that he rose from the dead, which means he is who he says he is, the son of God.
So, to be saved, you must believe in God and Jesus, and you must also try to follow God's rules and do good things in your life. If you do that, you will be forgiven for any bad things you did and you'll get to go to heaven. It's kind of like getting a ticket to a super fun party, but only the best-behaved guests get to go.
Remember, salvation isn't something you can earn by doing certain things. It's a free gift from God to anyone who believes in him and tries to live a good life.