Primitives (basic 3D shapes like cubes, spheres) are often "hidden" in Modeling 101 because beginner courses frame them as implicit starting points—even though they’re the fundamental building blocks of all complex models.
Nearly every 3D model begins with a primitive: You might turn a cube into a chair or a sphere into a character’s head. Courses prioritize teaching tools (like extrusion or subdivision) that build on these shapes, assuming learners will pick up primitives through hands-on practice.
If you’re new, try making a simple cup from a cylinder—this connects tool use to foundational concepts and shows how primitives form the base of detailed work.