This animation shows simple sharing. Each vehicle takes its own distinct route, stopping at each end destination to drop off both passengers. 

This animation shows multi-hop sharing. The two vehicles meet at a middle point, passengers exchange between cars, and each vehicle only stops at one destination. 

Transportation scientists reckon that multi-hop sharing would drastically reduce the distance vehicles would travel and so the amount of energy they require, and traffic they wuold generate. 

The diagrams below are a typology of ride share systems, showing the relationships between physical locaitons or stops vehicles would make.