1. Read The NEURON Book. If you can't get a copy of the book, go to the Documentation page and get the paper "The NEURON Simulation Environment" that we published in Neural Computation several years ago.
2. Check out the other links to papers and tutorials on the Documentation page.
3. For questions about hoc keywords, check out the programmer's reference, which is available online from a link on the Documentation page.
Hint to MSWin users: you already have the programmer's reference on your PC--click on the Documentation item in the NEURON program group (which is in MSWin's Start menu).
4. Many "how to" questions are answered on the FAQ (Frequently Asked Questions) page (hint: the link to the FAQ page is at the top of the Documentation page.
6. Still have a question? Time to post it to the appropriate discussion area in the NEURON Forum.