Is there a beginner's guide somewhere? This is something we'll want to do, but I'm totally lost in this conversation.
If you just do a search for Sorcerers of the Magic Kingdom, there will be several guides that pop up.
It's confusing written down, but when you get to the park, the CM will explain everything and it makes much more sense.
The jist of it is that Hades has recruited villains to help take over the Magic Kingdom and you, with Merlin as your guide, must travel the kingdom and defeat the villain using hero spells (cards)
The game is played at portals placed around the park (Main Street, Fantasyland, Adventureland, and Liberty Square/Adventureland), and the cards are used to cast spells. When holding the card up to the portal, the system will recognize it and spells specific to the character will be activated (Aurora has flowers, Lumiere shoots fire, things like that)
When you begin the game, you get a pack of 5 cards per person. There are 60 free cards total, and 10 that can be purchased. Every day you enter MK, you can pick up a new pack of cards and continue on the mission, but to pick up the new pack of cards, you have to activate the next portal in your mission (at the end of each portal, it tells you where to go next).
And I have to say it's a really irritating system. If the firehouse is the primary place to pick up cards, then you have to go deeper into the park to play a portal and then come back to get the cards. Sure, you can go to the one in Liberty Square, but (1) it only has one station and had a long line every time we went, and (2) it's more intuitive and convenient to pick up cards on your way into the park with a quick stop at the firehouse. I wish it worked like Goddesstree describes. That would be way more flexible and still force folks to keep playing the game to get cards.
I'm not discounting what you said, but I have never had an experience where Liberty Square had a longer wait than the Firehouse. Since less people know about it, you are far less likely to have to wait on first timers being trained. So while the line may seem long, it's usually just people picking up their daily pack so the line moves quickly. It has easy access to Adventureland, Liberty Square, and Fantasyland where 90% of the game is played, and it's out of the way so you don't have much curiosity traffic.