Fastbooting is flashing your phone with a stock file to get it back the way it was out of the box. You use RSD Lite or the RAZR Utility (my favorite) to flash the fast boot file
To get into fastboot mode, turn the phone off and hold the volume buttons while holding the power button. Then use the volume down button to highlight AP fastboot and press the volume up button to select it.
That isn't completely correct. Fastboot files do not format the entire memory and then re-flash every directory back to stock. Fastboot does do the important ones or the ones that cause you to get bootlooping (unless you're doing something you probably shouldn't be) If you look at mattlgroffs 1.6 utility post, he says cdrom and logo will fail at the top of the page ( ).
On a side note, you should use mattlgroffs util to fastboot to 181 as you need to remove the OEM commands from the xml file to avoid flash failure