How to model airplane in catia?

There are two ways. 1- Solid Modeling 2-Surfaces which can be done using Generative shape design and many other ways which i may not be aware of.

As Far as starting is concern, I always prefer starting with Nose cone, then fuselage, wings, tail and cockpit.

You can even start with Wings then follow up. Just be comfortable with what you start.

To proceed First have a blueprint of your desired aircraft.

Answered with a tutorial: https://grabcad.com/tutorials/how-to-model-airplane-in-catia

These dimensions may help you

simply use imagine and shape module to draw the fuselage... that is just like a china clay modeling.... you can drag any face in any manner.....

watch this https://www.youtube.com/playlist?list=PL9HaQnX7ItVFirI5X5r4llTKctg5RXzjl

might help. This is my first tutorial. Feedback is valuable.

How to design an aircraft without blueprints please provide an video