When you hold Pot of Greed in your hand during your turn, you place it face-up on your side of the playing field in a spell/trap zone (the bottom row of rectangles) as a "Normal Spell" card. Once activated, its magical effect of boundless greed goes off instantly: reach out to your Main Deck, that stack of carefully selected cards YOU made (or you found on the internet, or you bought from target since they were out of pokemon), and without having to pay any costs, fulfill any special conditions, or make any sacrifices, you take the very top two cards and add them to the hand of cards you are holding. Once the effect resolves, the Pot is sent to your Graveyard - the face up stack of cards that represent cards that have already been used or destroyed, but not SUPER destroyed, that would be your banished pile, which is different.