The bottom of your screen is the taskbar.
- far left = Start button
- quick launch buttons that open programs with one click
- far right = clock and notification area
Click on the shortcut to Libraries on the taskbar...
...which looks like this:
Go to Documents ...
You'll see a yellow bar pop up.
Don't click on the "X" in the top right corner of it, just click on it and choose "Don't show this message again".