The add task form can be used to add a task to the selected project. Simply type in a brief description for the task and select "Ok".
If you would like to add multiple tasks at the same time try holding down the shift key and pressing enter after you have entered a brief description for the task. This will add a task to the selected project but will not close the add task form. In this way you can quickly add multiple tasks to a project. You may also consider using the project wizard.