First, organize your ships. You can do it randomly or organize them by yourself.
If you decided to organize by yourself, click in one of the ships. The second click will or define the new position if your click is outside the highlighted (yellow) squares, or rotate your ship by clicking again in highlighted (yellow) squares.
After organizing, click on "Start Game" button.
There are four types of ships:
Hit all enemy ships (20 red squares) to win, good luck!