Screen scrolling is a glitch that causes Link to exit one side of an overworld screen and re-enter the same screen from the opposite side. This can be useful for increased travel speed, crossing obstacles (such as rivers), and even going through walls.
Stand near the edge of the screen. Link should be facing the edge, and be standing exactly 5 pixels from it. Once you are in position, press either direction on the D-pad perpendicular to the direction Link is facing for exactly one frame. For example, if Link is facing left or right, press up or down for a single frame. If done correctly, Link should turn around in place. Once he turns around, walk off the edge of the screen. Link will re-appear on the opposite side.