You can lock your screen while pressing Windows Key and "L" Key But you can create shortcut also to lock your computer screen in windows 7, vista and as well as in xp too.

• Right click at the specific place where you want to create a shprtcut.
• Select "New" And then select "shortcut"
  
• Now type exact "rundll32.exe user32.dll, LockWorkStation" in the given text box.
  
• This textbox will look different in "Windows xp" but it will work as same as it works in windows 7.
• Now give the name of this shortcut as i give it "Lock the computer screen of windows 7" you can give any name you like.
  

And you are Done. Now whenever you click on this shortcut your windows 7 computer screen will lock up. That is how you can create shortcut in windows 7 to lock your computer screen.

Now it depends on you from where you want to Lock on you computer screen. because to lock on your computer screen you have two ways now -

• You can lock now from pressing "Windows Icon" key And "L" key.
• Or you can navigate as my steps describle you with shortcut.