Blender is a dense program, and users often forget what a button does or discover a new menu. If you don't know what a button in Blender does, hover your mouse pointer over it. More often than not, a helpful tooltip pops up to concisely describe what the button does. And even if the tooltip isn't completely clear, you have a better idea of what to search for to get help.
And speaking of searching, one of the side effects of the event system refactor that was completed during the development of Blender 2.5 is the addition of fully integrated search. Using the search hotkey (spacebar) in a particular editor, you can type the name of the feature or tool you're looking for, and Blender shows you a list of operations that may match within the context of the editor that you're working in.