Eww. The ticks are here for a snack, and you're the snack. Click them before they embed themselves. If ten manage to latch on, you lose.
The controls are simple - click or tap the ticks to make them disappear before they dig in and get beneath the surface of your skin.
I made Tick Attack in a weekend as my first (and so far only) Ludum Dare entry a few years ago. The theme of the game jam was "beneath the surface." It was geared toward mobile platforms, hence the portrait style screen layout.