if its an I product

you can get a digitizer pen, there expensive but they make pin point precision on screen, but like all Macintosh you need to make sure it works for it.

otherwise they are these pens: http://www.ebay.com/itm/2-in-1-Metal-Capacitive-Touch-Screen-Stylus-Ballpoint-Pen-for-iPhone-iPad-Tablet-/262324715044?var=&hash=item3d13c57e24:m:m9MQOFOI4gBm1XXTfy2pHHw

its CHEAP but is like ok for arts, only thing is im always scared of these pens cause i keep thinking it scratches screen but the plastic tip is the same material as Wacom tablet pens. just don't press and drag on screen too hard. i have one myself but those pens SUCK if you got a cheap screen protector, there made for right on screen or those Liquid screen protector.

otherwise strongly suggest this for arts: http://www.ebay.com/itm/Artist-Brus.....8AAOSwZ8ZW~Vza

so there we have it, that is the best i can go for, otherwise you would need to go to a Mac store and buy a I pad digitizer pens, and as far price goes... better off getting a ACTUAL drawing tablet.

hope that helps.