This is a very unusual glitch that requires you to interact with the cartridge itself. When you come up to a character or object that's blocking your path (such as Mido or the Kokiri blocking the forest exit at the beginning of the game), you must pull up VERY gently on the left side of the cartidge. If done so correctly, the screen will become a bit fuzzy, and if you move forward, you can use this tme to walk through people and objects that aren't completely solid. This trick gives you access to portions of the game you wouldn't be able to get to until later.