How do you summon in Kingdom Hearts 2?

Answer 1

Look at your command menu in the lower left hand part of your screen. you should already have the attack command highlighted. use your arrow keys or analog stick and go over one. you should have a new menu with the summon command in it. when finished, you can go back up to the attack option, go over once and be back at the menu you started at.

Answer 2

If you go through the game normally u will get the spells.

Answer 3

Just play throught the game, you'll eventually get all the basic forms of the magic. To get all the advanced forms however, you have to explore a little bit.