After successful installation you can build a 'default city' with the City Wizard. This gives a very quick introduction to the CityEngine modeling workflow. In case you have not executed the City Wizard at the first start, it is described here how the City Wizard can be used.
HINT: The default 3D navigation works as in Autodesk® Maya®: press Alt together with left/middle/right mouse button for tumble/pan/dolly and the f-shortkey for framing selected objects.