Here's a short summary.
//sphere material size will bind to the current tool you are holding. This is useful for making hills, they will look rather ugly at first but do not worry, I will get to that later. You can also use //cyl material size to make cylinders. If you use air as material, you can easily remove circles of air and you could use that to landscape a bit.
The wooden hammer makes a region, region 1 and region 2. You can replace this region with air, to quickly form a cube of air. What I like to do is use //replace air air,sand and do that a few times, it will create a somewhat random terrain and later on I replace the sand with grass or stone, whatever you'd want.
Now, for the smoothing of the land. //smooth size will allow you to make the land smoother. This way you can turn those weird spheres into a nice terrain.
Look at this too.
