Okay kiddo, so think about when you go outside and play on a hot day. Your body gets really hot because it's working hard to keep you moving and having fun. When you get too hot, you start to sweat.
Sweating is your body's way of cooling down. It's like a natural air conditioning system! As the sweat comes out of your skin, it evaporates (which means it turns into a gas) and takes some of the heat with it.
Now, when people talk about "sweat of the brow," they're usually talking about a different kind of sweating. They mean the kind of hard work you do to make something new or to solve a problem.
Imagine you're trying to paint a picture. You have to think about what colors to use, where to put the paint, and how to make it all look good. It's not easy! You might have to work on it for hours or even days before you get it just right.
That kind of hard work is what we mean by "sweat of the brow." It's like your brain is working hard and sweating to make something new or solve a problem. Just like how your body sweats to cool you down when you're hot, your brain "sweats" when you're working hard to make something new or do something difficult.
So, "sweat of the brow" is a way of saying that someone worked really hard to achieve something. It's like saying they put in a lot of effort and it wasn't easy, but they did it anyway!