Basic actions are available from the tool bar on the left, but there are some more in the context menu.
There are many ways to organize your tasks, here is just one I used to develop Tasks plugin itself:
To track actual time, you have to turn that option in the plugin settings. They are available from IntelliJ IDEA settings.
Tasks tree appearance will be changed a bit, to show estimated and actual time. Also when you complete a task you will be asked
to enter actual time. If you turn this feature off, you won't lose actual time data, it will be just hidden.