TorDex’s home page is memorable for it’s bright promoted ads for marketplaces that fill the page. Anyone can leave an advertisement for a monthly fee in Bitcoin to maintain advertiser anonymity. TorDex also allows any webmaster to suggest adding an onion website to be included in its search results for free. Suggesting a website is easy; all you need is the URL of the onion website to include in the search results and fill in a captcha to verify that you're not a bot.
It's worth noting that TorDex search engine for the most part only indexes submitted sites. If you don't submit your website, it won't be crawled. Keep in mind that TorDex has a number of NSFW sites so browse with caution.