Robert, a short sale is a complicated process and something you should discuss with a local experienced agent and/or attorney. While I can get you an outline of what you need to do, it's best to discuss in person so that the people who will be helping you (the agent and/or attorney) can help you get the best information for you to make the right decision based on your particular needs.
A short sale is asking your lender, if you're the seller, to accept less than what is owed on the property in order for you to sell it to a buyer. There is a lot of paperwork required and it can be a fairly long process (3-4 months). You definitely want to stick with someone that is experienced in the process.
Each bank does their short sales a little differently, so it's important to know which lender owns the note. Also, there are various options that may be available to you depending on your situation, Like a HAFA short sale, that can help as well.