This is the box that you get when you purchase "SL Starter". Keep it safe because it contains your product code. If you ever need to find out what your product code is, or where to download the software again, just rez this box and then click on it. It will tell the owner (only) their product code and the location to go to download the software.
In addition it will also provide a quick link in a pop up box that will take you straight to the download page, with your information (Avatar name and product code) already entered. This is the easiest way to get the software, as it means that you do not need to type in your avatar name, or copy and paste the product code (although it would still be a good idea to make a copy of your product code, as you will need it when you install the software).