The basic principle of two strokes engines is that they mix the lubrication with the fuel for the engine.  Since gasoline has a much lower flash point it is ignited leaving the oil left behind to lubricate the engine components.  The number of strokes are a large difference along with the absence of valves in a two stroke engine.

Two-Stroke cycle theory

Two-stroke cycle means that two strokes of the piston complete one cycle.  In other words, the piston must move from TDC(top dead center) to BDC(bottom dead center) and then back to TDC in order to complete a cycle.  The two-stroke cycle engine completes a cycle each time the crankshaft completes on complete revolution.

The two-stroke cycle piston engine has activity on both the top and the bottom of the piston.  Gases are compressed on both sides; however, those compressed in the crankcase do not burn.  Instead, they move through the inlet port to the top side of the piston.

Most two-stroke cycle engines have no reservoir of oil in the crankcase.  Lubricating oil is mixed with the fuel.  When the air-fuel mixture enters the crankcase, the fuel and air form a vapor while the oil remains in droplets which cling to the components inside the crankcase.  These droplets of oil maintain an oil film on the inside of the crankcase and all the moving parts.  This film provide the necessary lubrication for the engine.