Okay kiddo, have you ever heard of the saying, "ignorance of the law is no excuse"? This is what ignorantia juris non excusat means in Latin. The law is like a big book of rules that everyone has to follow. But even if you don't know one of the rules in the book, you can still get in trouble if you break it.
Think of it like a game of tag. If the rule is that you're not allowed to touch the tree, but you accidentally touch it because you didn't know the rule, you still have to sit out. That's because the rule was still in place, even if you didn't know about it.
So, when it comes to the law, it's important to always pay attention to what the rules are so you don't accidentally break them.