Note: Both adding and editing a task is done in the Add/Edit Tasks dialog. Click the link for explanations of the tabs and fields in the Add/Edit Tasks dialog.
Use any of these methods to run the Add Task command to open the Add/Edit Task dialog (and add a new task):

Note: The Tasks menu on the Menu bar is the same as the Right-click menu except that it includes the Purge Completed Tasks command. Also Add a Template Task is greyed out when you're not entering a task in the Project View.
Note: If you are entering a task in the Project View, you will also see Add a Template Task; this command is not available in the other views.
You will see the Add/Edit Tasks dialog with no assigned date or time fields.
Then add the new task using the Add Task command as described above.
To add a task in the Weekly or Monthly Views, click on the desired day. (It will be highlighted with a white background.)
Then add the new task using the Add Task command as described above.
You will see the Add/Edit Tasks dialog with the date automatically filled in.
You will see the Add/Edit Tasks dialog with today's date in the Date field and the selected time in the Start Time field.
There are four ways to edit an existing task: