Topology for beginners
Topology is how your mesh is wired. It matters exactly as much as your project needs it to — no more.
The idea
Edge loops should follow the shapes you are building. If a cylinder is bent by animation, its loops need to run around the bend. If it never moves, fewer edges are fine.
When to relax
Static props for renders, 3D print models, background objects — topology can be simple. Characters and anything deforming need care.
Frequently asked questions
Do I need all quads?
No. Avoid ngons on surfaces that subdivide or deform; elsewhere, triangles are harmless.