How do you start up your Mac? I usually just hit the power button and then get to work. Once in a while, however, I need to start my Mac using special shortcut keys that force the Mac to modify its startup behavior.
For instance, you can hold down the option key and the OS X startup manager will let you select which disk to boot from. (This assumes you have multiple drives, each with an OS X system installed, or a Lion Recovery HD partition.)
There are quite a few more keyboard shortcuts that affect the Mac's startup process. For a list of these secret shortcuts, take a look at: