There are three available swords in The Legend of Zelda. The Sword, the White Sword and the Magical Sword.
Sword. The default weapon. It is given to Link by an Old Man inside a Cave. It is the weakest Sword in the game.
White Sword. The White Sword has double the Sword's power, but Link first needs 5 Heart Containers in order to obtain it.
Magical Sword. The Magical Sword is the most powerful of the three Swords that Link can use, doubling the attack power of the White Sword. It is found under a grave in the Graveyard during the First Quest, but Link requires 12 Heart Containers before he can obtain it. During the Second Quest, it is found in the mountains to the north, one screen to the left of where Link gets the White Sword.