Everything should be self explanatory.
If you need help anyway you can read through the Help page ingame.
(Available from the pause or main menu)
The main menu's background is playable btw.

Controls:

Move with WASD or the arrow keys.
Esc or Backspace will open the pause menu.
(Backspace is useful in the browser where Esc will end fullscreen first)
Restart from the pause menu.

Walkthrough: