2 stroke engines use a crankcase to pressurize the air-fuel mixture before transfer to the cylinder. Unlike 4 stroke engines, they cannot be lubricated by oil contained in the crankcase and sump: lubricating oil would be swept up and burnt with the fuel.
The precise 2 stroke oil ratio depends on your manufacturer’s instructions, as each engine can have varied requirements. If you put too much oil, it can generate additional carbon build-up, making it difficult to start the engine.
Marine and automotive engine oils are not interchangeable. The two primary reasons for this are water and wear. Consider that corrosion caused by water is a primary concern for marine engines.