You should help Choly to climb the mountain and reach its peak. But there are many places that you can fall down, so you should be very careful. Jump on the platforms and avoid falling by jumping over holes. You have normal and double jump and you should use them wisely to progress. There is also a time limit and you will lose the game if you run out of time. So you must collect the clocks that you find on your way to increase your remaining time and be able to climb higher.
Use mouse to play or Arrows on your keyboard. May work with AWSD & Spacebar keys as well.