The footprint will tell you how much space each component takes up in the DB. This is available in compressed and uncompressed reports. Item count will tell you how many items in the component are found.
Once you have identified which component takes up the most of your DB, for example com.ibm.team.build, you can run a deeper report on that component which will further seperate the information into build components.

Some tips for large DB:
-RTC will run item cleanups daily (sometimes frequently throughout the day) to help clean stale data. You can investigate increasing this task, or the expiration time of these items (located in Advanced Properties).
-You can also run the onlineverify to ensure the consistency of the data and that there is no corruption which may be preventing the item clean up from running.
-ensure all your builds are being pruned and any results cleaned up

Lastly, I would also recommend reaching out to your DBA and running a compact or reorg on the DB to ensure any empty space is utilized.