You can change your default values to automatically set your Tasks's due date to today. Go to Preferences > Default Values.
The due date is when the task is due and the start date is when you start the task. You can also have the start date automatically applied as a default value. This way the Task gets date and time stamped when you create it. This comes in handy, for example, when logging phone calls. And as a side note, the task will only show up in your calendar if it has a due date assigned.