The BuddyBar at the very bottom of the BuddySpace window is a set of status lights (none to start with) indicating key buddies/contacts of your own choosing. The idea is to provide a highly compact 'cockpit control panel' or 'radar screen', based on the Gestalt concept of a small number (say 3-7) of self-created lights which is very easy for you (and only you, as their creator) to identify at a glance. For example, in the set of six status lights below, I can tell at a glance that Joe Bloggs is in 'Do Not Disturb' mode, because I added the status lights myself and I know that Joe Bloggs is the 5th status light from the left.
You can float the BuddyBar off on its own (by pressing the Float/sailboat icon on the right), or bring it back (by pressing the Dock/anchor icon that replaces the sailboat). At any time, you can press the little 'Add status light' button (green plus sign with a small green dot in the upper right), and enter the Jabber ID (JID) of any user on your roster, or scroll through the popup list that appears in order to find them. They will then be added in sequence left-to-right, so you can track their presence easily. Right-click on any status light to delete it from the BuddyBar (they remain in the Roster of course until explicitly deleted from there!).