The plan pane is used to setup and configure work items.
Depending on your permissions, you may see all or some of tabs. The general and notes tabs are used to enter basic information about the work item.
In Personal mode the estimate tab is used to specify estimates for the work item. Estimates are used by the progress report to track work items.
In Enterprise mode the assignment tab is used to assign the work item to employees. Assignments are used by the progress report to track work items.
In Enterprise mode with Work Item Security enabled, the permissions tab is used to set user permissions on the work item.
The billing tab is used to define billing rates and define additional fixed cost items for invoicing.
Tutorial: Editing work items