As the ninjas climb down the ropes, guide them to the red door. Click and drag to create horizontal ropes that connect the vertical ropes. Ninjas will take every horizontal rope they come across. At the end of each level, you can shop for jutsu (special powers). Note: After you purchase jutsu, you cannot use it until you "equip" it. To do so, use the buttons on the left side of the Jutsu Shop. Once equipped, you can activate the jutsu by hitting the corresponding key (A, S, or D).
Hint: During the game, in the top left corner, there is an indication of when and where the next ninja will descend. Pay attention to this if you want to plan ahead.