Yaw is when we turn something around like a merry-go-round or a toy top. Imagine you are spinning around in circles like you do when you play. If you stop spinning around your feet, you are still looking in the same direction that you were before you started spinning. That direction is like the front of the toy.
A toy top spins around and around, but sometimes it starts to tilt to one side like it's going to fall over. If you keep watching, you'll see that the toy top starts to spin around in a circle while it falls over. That's what we call a yaw.
When something is flying, like a toy helicopter or an airplane, it turns left or right around its own center. That's also called yaw. So, when a helicopter turns left or right, it's using yaw to do it.
Yaw is used in many other things that turn in a circle, like a windmill or a turbine. When these things turn, they also use yaw to make sure they are facing the right way.