Here's a summary of the driving modes of the Porsche 918 Spyder:
E: Electric power mode, the V8 engine is only used when needed
H: Hybrid mode, the electric motor is working along with the V8 engine in order to provide the most efficient fuel consumption.
S: Sport Hybrid mode, the V8 engine's full power is used and the electric motor provides the boost for a stronger acceleration.
R: Race hybrid mode, the boost of the electric motors is further increased.
Hot Lap mode: The V8 engine as well as the electric motor work together in order to achieve maximum performance.
But it would be better if you watch the video below for more details.