You can create new tasks quickly by clicking on the New Task button. These tasks will be created in your Inbox. You can also press Command+N to create a new task.
If no project is selected then the new task will go to your Inbox. If you are working within a project and press Command+N, the new task will be created in that current project.
You can also click the + button in the project column or double-click anywhere below the + button. In both cases, a new task will be created for that project.
You can also create a new task by clicking on the Drop Down Menu on the Project Header.