Okay kiddo, so imagine you and your friend both want to play the same game, but your friend has a fancy toy to play with while you only have a regular one. Your friend might think that they are better than you because they have a fancy toy, but really, you are still just as important and valuable as they are, just because you are who you are.
The saying "a man's a man for a' that" is kind of like that. It means that no matter what a person looks like or how much money or power they have, they are all equally important and valuable, just because they exist.
So even if someone is really rich or really famous or really good-looking, they shouldn't think they are better than other people just because of those things. We should all treat each other with kindness and respect, no matter what.