For documentation we have docstrings for each function and tutorial-style docs (
http://docs.scipy.org/doc/numpy/user/,
http://scipy-lectures.github.com/intro/numpy/index.html) . All docstrings should have clear usage examples, but I'm actually finding it quite hard to find functions that don't have any right now. The only one I could dig up so quickly is corrcoef(). There must be a few more.
There are two ways to contribute to the docs, either send a pull request on Github if you familiar with git (or want to learn it), or use our doc wiki:
http://docs.scipy.org/numpy/docs/numpy.lib.function_base.corrcoef
In the doc wiki you can immediate see if the rendered version looks OK. You have to register a username and then ask on this list for edit rights if you want to use the wiki.
Besides those few docstrings that miss examples it's mainly the user guide that needs some work I think. For example the "performance" section is still empty. Filling that in will require some in-depth numpy/python knowledge though.
If you would like like to work on improving the documentation with examples, my suggestion would be to actually work on a part of scipy that interests you. We aim to get the scipy docstrings to the same level of quality as the numpy ones, and there's a lot to do there. Most docstrings miss examples, and some even miss more basic stuff (parameter/return value descriptions, formatting issues). This is a good overview of important docstrings per topic:
docs.scipy.org/scipy/Milestones/
Cheers,
Ralf