Either:
Right click on a item A container for a set of hierarchically structured information elements. These can be URLs to resources on the Internet, files or folders on the local file system. in your tree and select [New] and then [Task].
Left click on a item and select [New] from the main menu and then [Task].
Left click on a item and select [New] from the [File] text menu and then [Task].
Enter the title for the task.
Either double click on the new task in the tree or right click it and select properties..
Enter the details of the task.
If the task is repetitive click the [Recurrence] button and enter the details.
Enter a description of the task in the General tab
Click [Ok].
Tip: If the task is connected with an item in your tree create an association with it.