This is one of those meta-sim-sandbox-edu-tutorial-discovery games that are so common these days, but it's still tough to explain what you can actually DO, if not what it actually IS, so let me try to explain with a brief anecdote.
Years ago, my kids wanted a dog. They begged for some unspecified period of time, until one day we were driving along and saw a 'free puppy' sign at a farm. We stopped, and wound up taking home what the farmer told us was a 'purebred Welsh Olive Hound'. Thing is, when we took it to the vet for shots, we found out it was actually a toaster oven.
I guess what I'm trying to say is that Universe Sandbox looks like a game, but it's a lot more like a toaster oven. Everyone should have one, but it won't be fetching you any sticks.