Once you're in the Tor browser, use the search engine (hint: the double Mallard one) and type something like "top 10 darkweb marketplaces 2022". If it is legit, it will 100% be on that list. You then click on the marketplace and it should redirect you straight away. Because the Tor browser does not work like the usual search engine, it is difficult to find the right link among a lot of the mirrored marketplace sites that are scams so it is best to visit a site that's already done those security checks for you before they publish the best ones.