The Basic Workflow page gives a brief summary of the process.
For a more detailed workflow which covers most situations, see the following pages:
The Status Map page shows every state transition which is possible. Note that some paths are restricted to certain users.
The Patch Process page shows what happens to patches. A patch, which is a special kind of subtask in Jira, is attached to a bug and has its own workflow. The parent bug follows the same workflow as other bugs.