If a weapon has some special abilities like Daystar and other weapons I have, how do you "turn on" the special abilities.

It depends - If it is a permanent ability, such as permanent protection from evil, which I think the staff of the magi, it will automatically 'turn on', but if it is something like haste for 10 seconds three times a day, you can activate those by clicking on the backpack icon which is to the left of the quickitem slots. You can then choose whatever ability it is that you wish to use. This is also how you can use necklaces, or other items which have temporary abilities.