A ROM is basically a customized version of the Android OS. ROMs can offer performance tweaks and added features. It is always recommended to have a good battery charge before attempting to flash anything!
Alternative Wipe Option For Step 7 [easy]
The developer of the Android Revolution HD (ARHD) ROM, Mike1986, has made a Super Wipe script for the Galaxy Nexus. When you flash the Super Wipe script it will perform all the necessary wipes in step 7.
Mike1986 Super Wipe Script: Download Link / Mirror Link
Download the Super Wipe script to the phone before step 6 of this guide. The instructions below will replace step 7 above.
Flash the Super Wipe Script