"Vade retro satana" is a Latin phrase that means "go away, Satan." It's something people might say when they want to tell the devil to leave them alone.
In some religions, people believe in a being called Satan or the devil, who is supposed to be really bad and try to make people do bad things. So, if someone is feeling scared or bothered by something that they think might be connected to the devil, they can say "vade retro satana" as a way to tell him to go away and leave them alone.
It's kind of like when you might say "go away" to a bully who's bothering you at school. But instead of a person, it's telling the devil to back off.