Eat the dots. Eat the smaller players. Avoid the bigger ones. Press Space to fire half of yourself forward as an attack — gravity drags it back toward you, and after about 30 seconds it can merge again. Bigger means slower; smaller pieces of a split cluster trail in the water behind you.
Desktop: ↑ ↓ ← → to move, Space to split.
Phone: drag your thumb anywhere on the map to steer, hit the Fire button to split.
Bigger = slower, but you see further. Splitting halves your largest cell and shoots the new half forward — gravity pulls it back, and after 30 seconds it can merge again on contact.