Degreasing means you use a degreaser in a spray bottle. I used our degreaser at work called Magnum. In stores you can use Simple Green, or Meguiar's Xtra, or anything that is in a spray bottle. BE VERY CAREFUL spraying around high-polished aluminum (like exhaust tips or rims). Aluminum and alkaline (degreaser) don't mix well
It's important to use degreaser on the bottom half because that is where most road grime and dirt accumulate. This is the number one step in most cases.
-Darryl