Word is unable to display your entire document on your screen at a time. The scroll bars are very useful for moving around in your document.
Scroll bars also contain:
Scroll arrows 
The vertical scroll bar has the up and down arrow, and the horizontal scroll bar has the
left and right arrow. You can click on these with your mouse to scroll your
document.
Scroll boxes 
are on each scroll bar and indicate your position in your document.
Other items include:
View buttons 
are located on the left-hand side of the horizontal scroll bar at the bottom
of the Word screen. These allow you to change the view of your document.