http://aotskins.com/viewtopic.php?f=17&t=1050 - Useful place that gives links of important stuff which will help you.
Now if you want to post a skin, you go to the section which the skin belongs. Example: If you want to post a costume, go to the Costumes section. If you want to post different skins for male models, then go to the males section. Different skins for female model, goto Female section. Want to post both, goto Unisex section. Be sure to add screenshots for the skin you posted or your skin may get removed and you may get banned and be sure to check the rules of the site too :D
Happy New Year~