What this error means???

I tried to upload but instead i got this error:

Arduino: 1.6.5 (Windows 7), Board: "Arduino/Genuino Uno"

Moppy.ino:1:22: fatal error: TimerOne.h: No such file or directory
compilation terminated.
Error compiling.

I did everything like in the tutorial so idk why it wont work...
pls help me!!!

Which tutorial? Post a link.

Usually this will mean that a Library was not installed, or installed in the 1.0.x location even though you’re trying to use 1.6.x or something like that. Tutorials tend to get “stale” after a while.