Give your objects names in the attributes box, then use the icons at the bottom and the drop down menus to pick the particular object. There are the primitive icons and then off more to the right is where you can find meshes and groups. Naming stuff gets to be important when there are lots of things in a scene. You don't have to name them to use the icons at the bottom, but without names you'll get choices like rock1, rock2, rock3 etc. Sorry I'm too lazy to do a screen shot, give a holler if you need one and I'm sure someone will do one. HTH