People always try to sensationalize stuff about the deep web, often confusing the deep web with the dark web. Deep web means things that search engines can't crawl and index, like personal or company websites with no incoming links, anything behind a login screen. Deep web is largely 'secure data' housing. Dark web is that part of the deep web that is only accessible through special software like TOR(the onion router) or I2P or others. These software allow users and website operators to stay anonymous or untraceable by means of unallocated or otherwise unreachable IP ranges.
Dark web is pretty tiny portion of deep web by comparison, a bunch of pages with a lot of illegal content available like weapons, drug trading, porn, guns, PDFs on how to kill/build weapons/explosives, other controversial stuff like human testing and hit-man services. If you're interested just go ahead and check it out, download Tor browser bundle, install & run.
Dark web is 'super hard' to navigate, looking for websites that are still up while browsing through URLs that may or may not have been updated, resulting in dead links. There are search engines but nature of dark web is that, if something doesn't want to be found, it doesn't have to be. Best way around is to enter The Hidden Wiki and try to browse from there. It's a Tor based wiki with most of the major .onion URLs on it, just keep clicking links until something comes up. Usually it's a drug, weapon, hit-man or CP related (though most of the "hit-men" are bored teenagers).
There are some blogs and interest sites, most of which have anarchist or otherwise anti-government leanings. Some sites allows users to access academic research papers and eBooks for free on the dark web, sparking a raging debate as to whether academic papers should be free for all. Most of the expected illegal content is hidden behind paywalls, you won't get any of it unless you go looking for it and are willing to pay. There are normal sections of forums as well as sections with criminal schemes, how to's such as, lock picking, how to make a bomb, alarm deactivation, trade section with drugs, guns, restricted chemicals, fake diplomas, pirated software, expert hackers, online fraud, stolen credit cards & IDs, gory stuff, organs sale, child pornography, people talking about and organizing suicide, and a lot of drug and weapon sales. All with bitcoin and crypto-currencies.
Darknet Markets have an eBay-like rating system and discussion forums with people reviewing the wares, stealth and customer services. The money is held in escrow until customer is happy with the goods, plus it costs $$ to set up vendor account and anyone caught breaking the rules would lose this bond and all the money in escrow, making it safer than buying on the street.