If you’re curious about whether your computer is using the latest version of OSX, or how much available disk space you still have left, check out this screencast. Basic instructions are provided for checking both of those items.
Note that if you decide to update to the current version of OSX Lion (10.7.5), you should also check out the “Updating your Mac’s Software” and “Updating Java Software” screencasts. If you’re low on disk space, you should check out the “Accessing ADM Schools Network Storage” screencast.