The bug database is at http://krbdev.mit.edu/rt/ for normal read-only access. Some committers have write access to the bug database via the web interface, and can also update it by special commands in commit logs. The bug database also has an e-mail interface.
The easiest way to interact with the e-mail interface is to reply to messages that the bug database sends to the email@example.com mailing list. These messages can be copies of bug reports as they are submitted, or of replies to the bug.
If you are subscribed to the krb5-bugs mailing list, you may either reply or followup to a posting to add commentary to the bug or to follow up with the submitter. The bug database sets "Reply-To" to "rt-comment" and "Mail-Followup-To" to "rt". (both are at krbdev.mit.edu) The "rt-comment" address appends a comment to the bug log, while the "rt" address also copies the submitter. Make sure you retain the bug ID tag (the square-bracketed string in the "Subject" header), including the square brackets, or the server will reject your message.
The main queue that you are likely to want to look at is the krb5 queue.
We use a system of keywords to help us organize the bug database. (Need more details here.)
Committers can update the bug database by performing embedding commands in log messages of commits they make to the source repository. (Need more details here.)