In case you've never heard of the deep/dark web, it's a secret internet not accessible by normal search engines. It requires a modified computer or laptop to be accessed. It is estimated that the deep is about 500 times larger than the normal web. The public web is only the tip of the iceberg. If you could think of one thing that could happen, anything, I assure you, it has happened on the deep web.
The deep web offers complete anonymity, so therefor, you can say and do anything you like. It shows the true nature of the human mind: There are black markets, illegal pornography, drug and human trafficking, websites where you can hire assassins and hackers, and websites for murderers, cannibalists, human experimentation, and satanic rituals, to name but a few.
Not only this, but there are rumors that the government knows everything that goes on in the deep web, but simply chooses to ignore it. When they do take down a website, it usually appears again about two months later. Politicians use it, and there are conspiracy theories that the government doesn't destroy the dark web to keep the balance of the universe in check. (I think this is nonsense.)
The deep web is mainly a confusing mass of links, most of them leading to dead websites and outdated things. But if you do go on the deep web, one of the main things you shouldn't do is just go clicking on random links. This can be extremely dangerous. There are lots of YouTube videos about people's deep web experiences, and many are horrifying. Nearly every video warns NEVER to just click on random links.