The core of Bugzilla is the screen which displays a particular bug. It's a good place to explain some Bugzilla concepts. Bug 1 on Landfill is a good example. Note that the labels for most fields are hyperlinks; clicking them will take you to context-sensitive help on that particular field. Fields marked * may not be present on every installation of Bugzilla.
Product and Component: Bugs are divided up by Product and Component, with a Product having one or more Components in it. For example, bugzilla.mozilla.org's "Bugzilla" Product is composed of several Components:
Administration of a Bugzilla installation.
Anything that doesn't fit in the other components, or spans multiple components.
Creating, changing, and viewing bugs.
The Bugzilla documentation, including The Bugzilla Guide.
Anything to do with email sent by Bugzilla.
The installation process of Bugzilla.
Anything to do with searching for bugs and viewing the buglists.
Getting reports from Bugzilla.
Anything about managing a user account from the user's perspective. Saved queries, creating accounts, changing passwords, logging in, etc.
General issues having to do with the user interface cosmetics (not functionality) including cosmetic issues, HTML templates, etc.
Status and Resolution: These define exactly what state the bug is in - from not even being confirmed as a bug, through to being fixed and the fix confirmed by Quality Assurance. The different possible values for Status and Resolution on your installation should be documented in the context-sensitive help for those items.
Assigned To: The person responsible for fixing the bug.
*QA Contact: The person responsible for quality assurance on this bug.
*URL: A URL associated with the bug, if any.
Summary: A one-sentence summary of the problem.
*Status Whiteboard: (a.k.a. Whiteboard) A free-form text area for adding short notes and tags to a bug.
*Keywords: The administrator can define keywords which you can use to tag and categorise bugs - e.g. The Mozilla Project has keywords like crash and regression.
Platform and OS: These indicate the computing environment where the bug was found.
Version: The "Version" field is usually used for versions of a product which have been released, and is set to indicate which versions of a Component have the particular problem the bug report is about.
Priority: The bug assignee uses this field to prioritize his or her bugs. It's a good idea not to change this on other people's bugs.
Severity: This indicates how severe the problem is - from blocker ("application unusable") to trivial ("minor cosmetic issue"). You can also use this field to indicate whether a bug is an enhancement request.
*Target: (a.k.a. Target Milestone) A future version by which the bug is to be fixed. e.g. The Bugzilla Project's milestones for future Bugzilla versions are 2.18, 2.20, 3.0, etc. Milestones are not restricted to numbers, thought - you can use any text strings, such as dates.
Reporter: The person who filed the bug.
CC list: A list of people who get mail when the bug changes.
*Time Tracking: This form can be used for time tracking. To use this feature, you have to be blessed group membership specified by the "timetrackinggroup" parameter.
This field shows the original estimated time.
This field shows the current estimated time. This number is calculated from "Hours Worked" and "Hours Left".
This field shows the number of hours worked.
This field shows the "Current Est." - "Hours Worked". This value + "Hours Worked" will become the new Current Est.
This field shows what percentage of the task is complete.
This field shows the number of hours that the bug is ahead of the "Orig. Est.".
This field shows the deadline for this bug.
Attachments: You can attach files (e.g. testcases or patches) to bugs. If there are any attachments, they are listed in this section.
*Dependencies: If this bug cannot be fixed unless other bugs are fixed (depends on), or this bug stops other bugs being fixed (blocks), their numbers are recorded here.
*Votes: Whether this bug has any votes.
Additional Comments: You can add your two cents to the bug discussion here, if you have something worthwhile to say.