If you're worried about people snooping through your documents while away from your computer, worry no more. Locking down your computer is easier than you may think.
Step1
Hit the key with the Windows logo on it, and hold it down. (It should be two keys to the left of the spacebar, or near the left "Alt" key.) Step2
Hit "L." Windows locks the computer and requires a password to unlock it. Step3
Feel safe about leaving your computer.