When you start the car, the engine is cold. In this situation, there is much more unburned fuel which passes into exhaust. The catalytic converter is also still too cold to do anything. This is called cold-start emissions.

What you smell particularly strongly at that time is aromatic compounds from the gasoline. In chemistry, they were named "aromatic" precisely because they smell. A representative aromatic compound that is responsible for the exhaust smell during the cold start is benzene, although many of its derivatives are also present.

Incidentally, in many countries gasoline is called benzin/benzine.