M.A. does not know the rules of Magic. It simply keeps track of what cards are in your hand, in your library, in the graveyard, and on the tabletop. It lets you move the cards around, tap them, etc. Your opponent is responsible for making sure you do not cheat (such as playing a card without paying its casting cost, playing a sorcery during his turn, etc.) And you get to make sure that he doesn't cheat.

When M.A. starts up, it reads a database that contains the text of all Magic® cards.

First, use the New Game dialog to load your deck and then connect to an opponent across the internet (or any network, actually). Once you are connected, shuffle your deck (using the Shuffle tool on the toolbar), draw some cards (using the Draw Card tool), and start to play them.

To play a card (whether it's a creature, an instant, a land, or whatever), drag it from your hand to the tabletop. (If it's an instant or sorcery, you will have to bury the card after your opponent acknowledges that you played it.) To bury a card, drag it from the tabletop to the Graveyard tool on the toolbar.

To tap a card on the tabletop, click the middle mouse button on the card. To declare a card as attacking, click the right mouse button on the card, and select "Attack". To view a card's text, select "View Card" from the right mouse button menu.

That's really all there is to it. Drag cards around and tell your opponent, "I'm playing this." There are plenty of menu items, but they are all pretty self-explanatory.

Enjoy.