Perhaps you have a long document that you'd like to read all the way through without having to continuously press the arrow keys to move the insertion point. You can do that by scrolling, using the scroll bar.
The scroll bar is on the right side of the window, as shown in the picture. To use it, click the scroll box, and then drag it up or down to move through a document without moving the insertion point. Or click the single scroll arrows at either end of the scroll bar to move up or down.
To quickly scroll by using your keyboard, press PAGE UP to go up one screen or PAGE DOWN to go down one screen. You can try all this in the practice.