You are given the task to lock (finish) 100 boards filled with dots, impassable dots, keys and locks. You draw horizontal or vertical (no diagonal allowed) lines between 2 adjacent dots, thus connecting as many dots as you can without intersecting the lines. If you connect enough dots (shown on the ending yellow square) AND enter that square you will finish the level. However you get only 1 star. To get 2 stars you must connect even more dots, and to get 3 stars you must connect ALL dots.
On most levels you will encounter red, green or blue keys associated with RGB locks, and a special magenta lock, which is unlocked only if you have no key on you. You can have only 3 any keys on you at a specified time.
The game is controlled by your mouse. In addition you can move with WSAD or arrows keys, and restart with R key.