I used to play around a bit with 3D rendering and really basic animation but that's going back decades and it was nothing serious. Seems to me everything is based on either triangles or rectangles, to some degree. Even something like a cylinder is just a prism with many faces. I'm not sure how other effects work, like explosions, fog, smoke etc. I don't imagine they are tiny models as it would be super intense to render so it's probably it's own thing.