The version number is also important, but the biggest changes you will see are between different channels. The most important information in the image here is 'Second Life Server' that's the channel that you're on. (Just to the right of that is the version.) The image below shows you where in the help dialog to find the channel the region you're in is running. If the ground texture doesn't make it obvious, look at 'About Second Life' in the help menu where you will see a wealth of information about your own system, as well as about the server software running the region you are in. Some regions have a 'channel name' imprinted into the ground over and over again.
