Up arrow - move blade up
Down arrow- move blade down
Left arrow - move blade left
Right arrow- move blade right
No button needs to be used to use the blade. You just need to hover it close enough to the titan.
The number of red discs in the right hand corner will tell you which level you are playing.
If at anypoint in the game there are 3 breaches in the wall, you lose. You can repair breaches however throughout the game with the rock that spawns under the turtle. In this case, placing your dagger next to the turtle will not make you lose points and will actually let you repair 1 breach.
If you beat a level, you will be given the option to proceed to the next level. However, if you lose you must replay the previous level.
Your score is shown at the end of the game.
Sources:
https://easydraweverything.com/cartoon/learn-how-to-draw-colossal-titan/