A trace diagram is like a picture that shows you how something happens step by step. Let's say you want to make a peanut butter and jelly sandwich. You would start by getting two pieces of bread and putting peanut butter on one piece and jelly on the other. Then you would put the two pieces of bread together and cut it in half.
Now, a trace diagram would show you this process in a way that's easy to understand. It might have little pictures of bread, peanut butter, and jelly, and arrows that show you which step comes next. You could follow the arrows to see exactly how to make your sandwich.
Trace diagrams can be useful for lots of different things, like making a recipe, fixing a machine, or understanding how a process works. They help you see things in a clear and simple way, so you can understand them better.