Car modeling without blueprints!

How can i model car without blueprints.I heard about spline cage,but i cant understand how it works.Somebody knows about this method?
There is no special way to model a car without having true orthographic projections.
The best you can do is try get hold of photographs that are close. sometimes can be of model cars.

spline cage method just meant drawing out the curves of the body before you start modelling normally with polygon or nurbs. just look google images spline cage.

if you are really new to it, is best to practice with car that has blueprints. then when you can do that you can move on the more advanced without blueprints.