"dark web" is possibly easiest to explain with way youTube treats videos:
public is normal websites,
private is in between,
unlisted is your dark web
it is set of sites that do not pop up on normal search engines, but uses same platform as all the rest.
In order to access it i would recommend:
Fresh flashstick with small instillation GUI including Linux based OS,
use someone else's PC if possible, if not than get scrap computer you do not mind damaging.
there are several protocols and even supposed search-engines for the dark web that are listing once known sites. otherwise it works like normal internet with similar content tho not same % share. Some falsely claim it is filled with porn or hackers, i am more inclined to believe its bunch of governmental hackers (particularly USA, China, Koreas - in that order). But there is porn there just like on usual internet, some goods and services you can not get anywhere else yes.
Problem is that the whole website system as we know it makes your computer easy target even with VPN+antivirus. so be careful when dealing with darkweb just because these sites are basically unregulated, some contain trojan (no not the condoms), some contain worms, some are just there to bait people into installing X on their computer. because some people are scum.