A menu, just as the name implies, is a listing of available options from which to choose. Interesting isn't it how simple some things can become when one removes the expectation that something will be mysterious or hard to grasp and just looks at what is there.
As you might guess a menu can be on:
- the left,
- the top,
- the right,
- the bottom,
- the middle
- any combination of the above.
Admittedly some options are more common than others. This has not always been so. In the beginning there weren't many menus. "What no menus?" you say. Nope, pages were text with hotlinks embedded in the paragraphs as they occurred. Later the bottom menu and top menu came into vogue. Then after tables and their formating possibilities were introduces the side menus came into being.
Web pages as you seem them now are a fairly recent invention. Don't forget that it has not always been the way it is now, nor will it always be the way it is now. Be prepared to 'mutate with the flux.'