The dark web is basically just websites that Google and other search engines will not index and rank in their search engines due to likely illegal activity going on at those websites.
The sites on the dark web typically sell illegal things such as counterfeit money, drugs, hacking software and a lot of other things.
To access the dark web you would use software such as TOR software to access the TOR network where the dark web is located.
The TOR software is free software that can be used by anyone wanting to access the dark web.
I'm inclined to try it myself but doubt I will as I don't want to risk getting into any trouble even though I likely wouldn't get into trouble.