Each school has at least one minion, here are the levels that the minions are available through a quest.
Fire - level 28 Ice - level 28 Death - level 28 Storm - level 18 Life - level 18 Balance - levels 18 and 38 Myth - levels 2, 7, 18 and 38
Once you earn your minion, it will appear as a card that you must put in your deck. Once the card is in your deck, it becomes available as one of the cards that appear when you are in a duel. Casting the spell (when it appears, and you have enough pips) will summon a creature to assist you in the duel.
If you want the prize, you have to build the ladder rung by rung. There are no shortcuts.
Also, the game has what are called Henchmen. These can be hired (summoned) while in a battle.
Henchmen don't work for free. They charge from 20-50 Crowns, depending on their level and they will leave after the battle is over (they don't follow you to another battle or to the next floor of a dungeon/instance).
You can access Henchmen from the Crowns Shop (upper left corner of your screen). Once summoned, the battle timer will reset to 30 seconds, so you have time to plan your next move. You can hire as many Henchmen as you have room for on your side of the battle circle (up to 3 if you're alone).
Henchmen can make some of the tougher boss battles easier. They're useful if you're having trouble with a certain boss and can't find any players to help. Although I never used any on my Life Wizard, I find myself sneaking one in here and there on my newer wizards.
When you use the Crowns menu for Henchmen, I recommend that you use the List (the three lines in a yellow circle) option and sort them by clicking on "Name", so that you can find what you want more easily.
When you hit a certain level, you'll get a message from your teacher and it will say "come to me for your next spell." Then you have to do a quest, and you will get your Minion Card.
"With the power of Fire, Ice, Storm, Myth, Life, Death, and Balance, you will win. Flames apon your eyes, seal the frost, control the sea's, summon creatures by memorizing their true name, healing to victory, stealing health, and blading, with the power...A true Wizard can be. Bring A Wave in your life! WaveBringer."