Don't expect it to behave like a PC keyboard, expect it to work like a Mac one.
The order of the keys on a PC keyboard, when connected to a Mac (starting at the space bar, moving left) is usually Option, Command, Control. You'll use the Option key to make extra characters.
Also be sure to familiarize yourself with the Key Caps program (in the Apple menu in OS 9 and earlier, in the Applications folder in OS X 10.0-10.2, and in the Keyboard menu as "Show Keyboard Viewer" in OS X 10.3), which shows you what happens to the keyboard as different modifiers are pressed.
tooki