Firstly, don't be put off by the name. The Dark Web is simply a network of websites which requires basic encryption technologies to access. Most of us will use these technologies everyday to check our bank accounts and email. Many people will think that it is only the haunt of drug dealers and those who peddle stolen information. Nothing could be further from the truth. Many professionals use the Dark Web and the list includes law enforcement, journalists and cryptologists. It is also used in countries where free speech is suppressed, giving dissidents an opportunity to express themselves.
The main difference between the Dark Web and the clearnet is that the former requires security tools to make web traffic as anonymous as possible. The way to access it is via the Tor security suite and the Tails operating system. Tails, which is Linux based, is an ideal layer of additional security being portable and booting from a flash drive.
Nowadays hackers, leaked information and general carelessness with data security abound, and on the Dark Web is where it will end up. This has become inevitable due to the user and server anonymity which it provides. Admittedly there is a lot of bad stuff out there on offer, the most infamous of which having been Silk Road. However, the existence of the Dark Web allows investigative news organizations such as ProPublica to communicate securely with sources. Even Facebook is there with over a million users a month.
There can be some confusion existing between what constitutes the difference between the Dark Web and the Deep Web. The latter simply are pages which are not accessible to the public such as corporate intranet, secure bank pages and private social media accounts. These pages are non-searchable.
Communication between Dark Web operators would usually be in PGP email encryption or encrypted webmail services. If you see a .onion, this indicates that it is a Dark Web URL and the required security plugins will be required to access it.
Whilst it hits the headlines quite often for the wrong reasons, the Dark Web doesn't have that many sites. Hard to estimate but somewhere between 10,000 and 100,000 active ones. Sites come and go as they are discovered and removed by law enforcement.
Many law abiding citizens are supportive of the Dark Web as it promotes anonymity and, most importantly, privacy. Rather than a haven for criminals, it can be seen as a force for good.