all materia: you have one star, you'll use ALL one time per battle. 2 stars, twice per battle, and so on, until you master it, then you can either sell it for 1.4 million gil or use it for unlimited times per battle.

enemy skill: have it equipped on anybody. a monster has to use the enemy skill on the person who has it equipped for the materia to learn it. you can either wait for the monster to attack that character or manipulate the monster and control it to attack the character. make sure the character doesn't die from that attack.