Complete walkthrough of writing setup.py scripts here. (with some examples)
If you’d like a real-world example, I could point you towards the setup.py scripts of a couple major projects. Django’s is here, pyglet’s is here. You can just browse the source of other projects for a file named setup.py for more examples.
These aren’t simple examples; the tutorial link I gave has those. These are more complex, but also more practical.