Bug tracking CAN be
of things.
At it's most basic, it's someone (could be anyone) submits a bug, with a detailed description. Many bug trackers enforce a minimum of infoirmation (sometimes customizeable) like, make and model of PC, ram, video card manufacturer, video ram, build number, etc.
That information goes into a database of some sort, and sometimes manually, and sometimes automatically, gets assigned to a developer for.
Some bug trackers email you when you have bugs, some don't, it gives you a way to keep track of how many issues you have that are considered yours (for instance, we might have one person doing all the openGL fixes, another doing sound), give you (and others) a way to track what has been done with an issue (has it been confirmed, can it be reproduced, if so, was it easy to fix? does it need to be reassigned to the person who originally wrote the code? is there a plan to fix it at all?) how bad the issue is (crash bug, kills the whole PC? or is it a little thing like a graphic is a pixel off?).
Anyway, a central place to see what needs to be worked on OUTSIDE the design document and adding new features, so, anyone involved in the project can get a "state of the union" on the projects health.
Clear as mud?