I recommend that you talk to someone when you get a chance to get all the information regarding your situation. There is a lot more to understand that simply what it means. Every situation is unique, and no 200 word answer will be enough to really understand what it means, the process or the implications of a short sale.
Not just any agent will do. You need someone who has experience not only with short sales, but also with your bank. Every bank has their own process and procedures as well. If an agent tells you that it is all pretty much the same, they are mistaken. If they say it can take 3-4 months that is an average, and may not necessarily be true. Some smaller banks have been know to approve shorts sales in a couple of weeks time, and the house is sold 30 days later. Some take longer. You want to be prepared.
Again, it is a process to get answer to all the questions. This being the first. Good luck, and as mentioned here - stay in communication with your banks.