You’ve got a moose, in a tiny hard hat, pulling a cart that has a saw attached out front. You harvest gems and take them back to be ground into dust, which gets taken away by rail to earn currency. You spend that currency for more lanes, more moose, and better equipment.
There isn’t really much more to say, it’s a simple idler, number go up, the demo doesn’t give any impression that there is really any additional systems or story to come later. Just work on clearing the map of gems.
If you’re looking for a video playthrough, Real Civil Engineer did one a while back. The Moose Miners demo is still up on their Steam Page, with the developers aiming for a Q2 2024 release.