1 Slightly used from home to seal the cylinders – forms the top of the combustion chamber so the engine can build compression.
2. Controls airflow – Houses the valves, ports, spark plugs/injectors that let air/fuel in and exhaust out.
3. Cools the engine – Contains coolant and oil passages to pull heat away from combustion.
Basically: it’s the lid that seals the engine, handles breathing, and keeps it from overheating.