Only the electric motor drives the drivetrain, and the ICE works as a generator to power the electric motor or to recharge the batteries. The battery pack can be recharged from regenerative braking or the ICE.
Series hybrids usually have a smaller combustion engine but a larger battery pack compared to parallel hybrids, making them more expensive than parallel. This configuration makes series hybrids more efficient in city driving. The Chevrolet Volt is a series plug-in hybrid. However, GM prefers to describe the Volt as an electric vehicle equipped with a “range-extending” gasoline-powered ICE as a generator and therefore dubbed an “Extended Range Electric Vehicle” or E-REV.