Exemplar theory is like having a bunch of toy cars. You have a red car, a blue car, and a green car. Now imagine that every time you see a car on the road, you compare it to your toy cars to figure out which color it is.
Exemplar theory is like that, but for your brain trying to figure out what things are. Your brain compares things you see or hear to other things it has seen or heard before, called "exemplars." For example, if you see a blue bird, your brain compares it to all the other birds you've seen before to figure out that it's a blue jay.
The more exemplars your brain has to compare to, the easier it is to figure out what something is. And sometimes your brain might even use a mix of different exemplars to figure something out.
So, next time you see a bird or a car, remember that your brain is working hard to figure out what it is by comparing it to all the things it's seen before.