Sometimes called Elder Dragon Highlander (EDH), Commander is a format where you have a legendary creature (your commander) at the head of a 100-card deck based around it. All the cards in the deck must have the same "color identity" as the commander and you can only play one copy of each card (except basic lands). The format is also multiplayer as opposed to 1 vs. 1 and you start with 40 life, making this format radically different from other Magic: the Gathering formats.
These cards cannot be used in this format:
Ancestral Recall · Balance · Biorhythm · Black Lotus · Braids, Cabal Minion · Channel · Chaos Orb · Coalition Victory · Emrakul, The Aeons Torn · Erayo, Soratami Ascendant // Erayo's Essence · Falling Star · Fastbond · Flash · Gifts Ungiven · Golos, Tireless Pilgrim · Griselbrand · Hullbreacher · Iona, Shield Of Emeria · Karakas · Leovold, Emissary Of Trest · Library Of Alexandria · Limited Resources · Lutri, The Spellchaser · Mox Emerald · Mox Jet · Mox Pearl · Mox Ruby · Mox Sapphire · Panoptic Mirror · Paradox Engine · Primeval Titan · Prophet Of Kruphix · Recurring Nightmare · Rofellos, Llanowar Emissary · Shahrazad · Sundering Titan · Sway Of The Stars · Sylvan Primordial · Time Vault · Time Walk · Tinker · Tolarian Academy · Trade Secrets · Upheaval · Yawgmoth's Bargain · todas las cartas ante/conspiracy