There are several ways to create a new issue in JIRA. Here is one of them:
Go to the project home page. For example http://jira.jboss.com/jira/browse/JBTPL.
Click on "Create a new issue in project ..."
The next page displays a form with the issue fields.
Enter a descriptive issue Summary
For some projects, there will be a Security Level field. It controls who can see an issue. See What is Issue Level Sevurity?.
Select a Priority
Avoid setting Due Date unless it is necessary. Prefer work estimates to due dates, because it allows more flexibility in arranging tasks within a version.
Select the most specific project Component/s that the issue applies to.
Affects Version/s is optional. It provides information about the versions affected by a given issue.
Fix Version/s is an important field. It specifies what versions address the issue. This is the field that determines whether an issue will show in project roadmap and release notes.
In the Assign To field, select the person the issue should be assigned to. Select Unassigned if you haven't decided who to handle the issue. Select Automatic for JIRA to assign the issue to the default assignee (configured by the project administrator).
Environment applies to Bugs and should be populated with details about the hardware platform, OS, JVM and other relevant information that would help reproduce the environment where the bug occured.
Description should be used for detailing the nature of the issue. In case of a bug there should be specific instructions how to reproduce the bug.
Original Estimate must be filled in to provide an approximate sizing of the issue.
JBoss Forum Reference can be optionally populated with a link to a related discussion that generated the task.
After filling in the form, click Create to submit the issue.