As well as the standard buglist, Bugzilla has two more ways of viewing sets of bugs. These are the reports (which give different views of the current state of the database) and charts (which plot the changes in particular sets of bugs over time.)
A report is a view of the current state of the bug database.
You can run either an HTML-table-based report, or a graphical line/pie/bar-chart-based one. The two have different pages to define them, but are close cousins - once you've defined and viewed a report, you can switch between any of the different views of the data at will.
Both report types are based on the idea of defining a set of bugs using the standard search interface, and then choosing some aspect of that set to plot on the horizontal and/or vertical axes. You can also get a form of 3-dimensional report by choosing to have multiple images or tables.
So, for example, you could use the search form to choose "all bugs in the WorldControl product", and then plot their severity against their component to see which component had had the largest number of bad bugs reported against it.
Once you've defined your parameters and hit "Generate Report", you can switch between HTML, CSV, Bar, Line and Pie. (Note: Pie is only available if you didn't define a vertical axis, as pie charts don't have one.) The other controls are fairly self-explanatory; you can change the size of the image if you find text is overwriting other text, or the bars are too thin to see.
A chart is a view of the state of the bug database over time.
Bugzilla currently has two charting systems - Old Charts and New Charts. Old Charts have been part of Bugzilla for a long time; they chart each status and resolution for each product, and that's all. They are deprecated, and going away soon - we won't say any more about them. New Charts are the future - they allow you to chart anything you can define as a search.
Both charting forms require the administrator to set up the data-gathering script. If you can't see any charts, ask them whether they have done so.
An individual line on a chart is called a data set. All data sets are organised into categories and subcategories. The data sets that Bugzilla defines automatically use the Product name as a Category and Component names as Subcategories, but there is no need for you to follow that naming scheme with your own charts if you don't want to.
Data sets may be public or private. Everyone sees public data sets in the list, but only their creator sees private data sets. Only administrators can make data sets public. No two data sets, even two private ones, can have the same set of category, subcategory and name. So if you are creating private data sets, one idea is to have the Category be your username.
You create a chart by selecting a number of data sets from the list, and pressing Add To List for each. In the List Of Data Sets To Plot, you can define the label that data set will have in the chart's legend, and also ask Bugzilla to Sum a number of data sets (e.g. you could Sum data sets representing RESOLVED, VERIFIED and CLOSED in a particular product to get a data set representing all the resolved bugs in that product.)
If you've erroneously added a data set to the list, select it using the checkbox and click Remove. Once you add more than one data set, a "Grand Total" line automatically appears at the bottom of the list. If you don't want this, simply remove it as you would remove any other line.
You may also choose to plot only over a certain date range, and to cumulate the results - that is, to plot each one using the previous one as a baseline, so the top line gives a sum of all the data sets. It's easier to try than to explain :-)
Once a data set is in the list, one can also perform certain actions on it. For example, one can edit the data set's parameters (name, frequency etc.) if it's one you created or if you are an administrator.
Once you are happy, click Chart This List to see the chart.
You may also create new data sets of your own. To do this, click the "create a new data set" link on the Create Chart page. This takes you to a search-like interface where you can define the search that Bugzilla will plot. At the bottom of the page, you choose the category, sub-category and name of your new data set.
If you have sufficient permissions, you can make the data set public, and reduce the frequency of data collection to less than the default seven days.