When you create a new trip, you can choose which trip type it is. The trip type is used, among other things, in the generation of routes.
Used when you have neither car or anything else. Routing is done in pedestrian mode.
Used when the majority of the trip will be run by car. Routing is done by the best executable road.
Used when the main means of transport is bicycle. Routing is done in bicycle mode.
Used when the main means of transport is skiing. Routing is done in pedestrian mode.
Used when the main means of transport is boat. Routing is done in pedestrian mode.
Used on longer trips, usually by plane. Routing is done in pedestrian mode.