I recently bought a new (to me) MacBook Pro with Lion installed. The previous owner hadn’t had the time to completely wipe everything from the machine since I bought it 3 hours after I first responded to his Craigslist post. So, I found myself in need of starting completely fresh and Googled it. I found some disjointed posts in various Mac-related forums, but nothing that said “This is how you do it”. So, this is how you do it:

1. Restart your Mac and hold down the Command-R. That will open up the “Mac OS X Utilities” app (seen here).
2. Select “Disk Utility” from the menu and proceed to erase the Macintosh HD drive. This completely wipes the Macintosh HD drive, so be really sure you want that to happen.
3. When Macintosh HD is erased, quit the Disk Utility app and select “Reinstall Mac OS X” from the Utilities window.
4. The reinstallation process is pretty well thought out, so it will guide you the rest of the way through.

This may not seem like much, but I couldn’t find anywhere that explained the whole process.