Alright kiddo, so you know how sometimes you make something really cool like a picture or a story or a song, and you want to make sure people don't copy it without asking you first? That's what copyright is all about.
But sometimes, it can be okay for people to use parts of your cool thing without asking you. That's where fair dealing comes in. Fair dealing is a rule in Canadian copyright law that says if someone wants to use part of your cool thing for certain reasons, they don't have to ask you first.
Those certain reasons are pretty special, though. They're called "fair dealing purposes," and they only apply in certain situations. For example, someone might be allowed to use part of your cool story if they were writing a review of it, or if they were teaching a class about it.
But even then, they can only use a small part of your cool thing, and they have to give you credit for it. It's kind of like sharing a toy with your friend - you can play with it together, but you have to take turns and give it back when you're done.
So that's fair dealing - it's a way for people to use parts of your cool thing without asking you first, but only if it's for a good reason and they're not taking too much of it.