Google search terms: simple origami, dollar bill origami, origami paper airplane, origami toys
Buying paper: Not widely available in stores, even craft stores as of late. Use normal computer paper in a pinch, or order a wide variety of origami paper packs from Amazon, Etsy, and more.
Tips: the more complex a pattern, the thinner the paper should be for ease of folding! Watch videos of the origami you are trying to fold - sometimes those little pictographs are not good enough! If your paper is too thick for your model, try using a larger sheet of the same paper!
Google search terms: modular origami, sonobe unit, sonobe variation, Toshi’s jewel, spiked pentakis dodecahedron
Books: Marvelous Modular Origami by Mukerji
Polyhedron Origami for Beginners by M Kawamura
Tips & Tricks: Use computers paper for large modular origami, instead of thinner origami paper. Modular origami is held together by friction, and so thicker paper will provide a tighter model that is easier to put (and keep) together!
Origami + Engineering
Google search terms: origami satellite, origami nanotechnology, DNA origami, origami engineering, math of origami
Videos: Engineering with Origami by Veritasium (YouTube)
The Math and Magic of Origami by Robert Lang (TED, YouTube)