Your touch sensitive screen works as well. When you are selecting spells there is an icon you can select that lets you practice casting. If you draw the symbol correctly on your screen with your finger or stylus the spell icon will appear.
When you duel you will have a 10 second window each cycle to fill your 5 slots with what ever combination of spells will fit and us within your heat build up limit.
Hope that helps some,
Magus of the 16th Circle
Fellowship of Wizardry
Season One Division III Champion