Dark Web is the virtual equivalent of a black market. Like Silk Road that marketed illegal drugs through the Dark Web, entities which want to operate out of the arms of the law seek refuge in the Dark Web. Dark Web can be simply explained as a specialised form of browsing in incognito mode. While incognito mode disables browsing history and web cache, the Dark Web is shielded by specialised software such as Tor. As it is evident by the name, the USP of a Dark Web site is the anonymity it offers and the near-impossibility of tracking it down.
The near-unanimous opinion is to stay away from the Dark Web because it is inherently unsafe. It is so easy to lose your way, and valuables such as money and data in the Dark Web. Unless you fear prosecution by an authoritarian regime or a government agency for doing something you think legitimate, the Dark Web should be a no-go area.