Instructions: use the arrow keys to move.
You can also pause the game with 'p', reset a level with 'r', mute the sfx with 's', or mute the music with 'm'. The mute buttons can be troublesome at times though, so don't play around with them too much ;)
The rest is explained in the game, when you need it.
You can read a longer and more thorough description at Newgrounds:
And/or watch the video tutorial:
(Don't ask me why some of the text is in bold, as I have no idea :/)