The only thing you really need before you can play Magic: The Gathering is a deck of MTG cards.
There are intro packs, which are sets of 41 cards and a booster pack, to give you a good starting deck. Or, you can just buy several booster packs to get a more random assortment of cards. But you might not have sufficient lands to cast the spells that you get, so be warned.
Use the Wizards of the Coast Locator to find stores near you that carry MTG cards.
You should probably have at least 40 to 45 cards in your deck to play the game. The official rules say you need to have at least 60. Also, you are not allowed to have more than four of any card in your deck, except land cards.