Scrolling is the act of moving the scroll bar in a program's active display window. The scroll bars on the right-hand side and bottom of the screen in most GUIs have a pair of arrows pointing up and down or left and right, respectively. You can click on the arrows to move the information in the screen in the desired direction. This allows a user to see beyond what appears in the initial screen of a Web page.
The content that appears on the initial screen is above the fold and the content you see when you scroll down is below the fold. One thing you don't want to do as a Web designer is develop a Web site that requires users to scroll sideways in order to view the content, because scrolling sideways is a PITA.