All you have to do is install the application and the Start button will return to its place as though it never even left. You'll still be able to access the Metro desktop if you want to, but you don't have to.
Although Windows 8 has no Start menu, all of the programs still create corresponding direct access, so this application really isn't doing much more than showing you what's on your computer. You'll be surprised to find that everything is there, like it had never left.
Of course, the menu is completely configurable and you can adjust its aspect so that it adapts to your needs. This is an excellent way to take advantage of the improvements included with Windows 8 without losing what has always been one of Microsoft's hallmarks.