Okay kiddo, do you remember when we played with the water hose and you twisted something to make the water come stronger or weaker? Well, a wastegate is like that twisty thing, but for a car's engine. It controls how much air goes into the engine to make it go faster or slower.
When the car goes really fast, the engine gets hot, and we don't want that to happen because it can damage the engine. So, the wastegate helps by letting out some of the extra air, kind of like releasing some pressure.
Think of it like blowing up a balloon. If you don't let some of the air out, the balloon will pop! The wastegate helps the engine release the extra air so it doesn't "pop" or break.
So, that's what a wastegate does, it helps control the air going into the engine so it runs smoothly and doesn't get too hot. Pretty cool, huh?