Hiya. If you download Rebel's Sonic pack, which is a LHA file, you just need to extract it to your hard drive somewhere. It actually includes Backbone and all the files you need to build the Sonic game, so once it's extracted you would open the drawer and run Backbone, then open a project from the menu and select the Sonic project.
From there you can edit the levels, blocks and objects, and compile the game from the menu.
If you downloaded the full Backbone package as well as the example games there is a tutorial included as well as a bunch of example graphics and objects you can use to make your own games.
