Fillet, Chamfer and Shell
1. Before you can use Fillet, you need a 3D object with some kind of edges (so no spheres). Click Fillet. Fillet is very straightforward--type in what radius you want to use (if you make it too big, it will not work!) and then click on the edges you want rounded. Then hit ok.
2. Chamfer is just like Fillet, only it shaves the edges off at about a 45 degree angle. Click Chamfer, select a distance, and click on the edges you want.