Go to the Audiogon homepage There is a yellow band across the top, hover the pointer over Learn and a grey band will appear below it. In this band will be two icons, Selling on Audiogon and Buying on Audiogon. You know what to do next.
Also, at the bottom of the Homepage or the Selling on Audiogon page in white lettering on a black background there is a link to a Selling Checklist. More information there. Further, at the bottom of the Selling Checklist page there are links to articles with more information about selling on Audiogon.
If you have any questions after reading the guides and articles, feel free to ask them on the forums. Good luck!