I would like to promote what I think is the ultimate source of this kind:

The Greatest Paper Airplanes[1], a virtual interactive encyclopedia for Windows 3.1

Of course, you can use it in the browser these days[1].

It goes through basics and history of flight, basics of paper folding, and gives you dozens of interactive, animated, step-by-step designs.

Loved it as a kid, and was thrilled to see it preserved online.

[1]https://classicreload.com/win3x-greatest-paper-airplanes.htm...