This is just a quick guide on the issue possibilities and the original content used as reference can be found on the Atlassian support site.
An issue represents an action that has to be done. That action can be a task, a bug, a feature request, or any type of action your organization might need to work with. Issues are the core of the Jira applications since all the team collaboration happens around the work items and their organization. It is possible to customize issue types creating issue sets associated with projects, and even per permission types.
If you're ever around a project manager for longer than 45 seconds — you've more than likely heard them ask you to "workflow your tickets". The first time, you may smile and nod politely and think "what in the world does that mean?"
What they're asking you to do is update the status of any tickets you're assigned to. This is actually really important because it helps the number crunchers understand how long the pieces of a given process take, and where and when bottlenecks are occuring.
For an in-depth look at all the issue statuses — please take a look at Atlassian's documentation.