Most instructions in the game. Press the space key to move up. The cat will move down when you are not pressing space. Don't touch the pipes or the green stripes on the top or bottom of the screen. Easy only has pipes. Medium has pipes and a floor. Hard has pipes, a floor and a roof. Too hard? try the practice version.( I can't get the hyperlink to work, so go to my page and look for 'flappy cat test rink' in the projects!!)
This game is obviously based on Flappy Bird, so I give them credit for my inspiration. I also give scratch credit for the 'scratch cat' sprite