You’re a snake. Aim with the mouse (or drag a finger). Eat dots to grow. Touch another snake’s body — or a wall — and you’re done. Hold Space (or the Boost button on phones) to sprint — costs a little length, drops the rest as crumbs.
Desktop: aim with the mouse, hold Space or click to boost.
Phone: drag your thumb anywhere on the map to aim, hold the Boost button to sprint.
Spawn protection is brief; it lifts on first boost.