I'd avoid it like the plague, I understand it's used by some less than nice individuals.

Be careful when using the Tor browser and the dark web. You don't really want to attract the attention of the agencies (assuming you're all whiter than white, of course). Don't use your normal PC unless you regularly clean it.

Ok I'll try. The web operates at different levels : surface web - what we all know,eBay,Amazon,Google results etc etc,then there's deep web - this is basically stored data that doesn't come up on google results and can contain pretty much anything - were talking insurance quote records,old cinema listings,backdated music catalogues etc etc...
Then there's the dark net - this is accessible through specially designed browsers that route traffic in a circular fashion making it difficult and time consuming(but not impossible) to track the user. Content here might include things like Silk Road(a drugs marketplace),guns and weapons for sale and those naughty terrorist types use it for recruitment and promo videos. Etc etc...you get the idea.
It's called dark web as you have to make a serious effort to access it - you don't just stumble upon it with a squiffy keystroke. How it operates : servers in hicky places(Eastern Europe,Middle East,who knows where)will,for money,pretty much allow people to post up anything and are difficult(but not impossible) to track/shut down.
currency used is Bitcoin(mainly) : again marketed as untraceable but it's not. TOR browser is used - again traceable but it's difficult and time consuming and will flag your computer if you use it.
If you are looking for guns/drugs/terrorist know how this is where you go.
THEN - there's Marianna web. This is as deep as it gets and very few people can access this. It gets bad here. This is kiddie porn sharing,snuff movies,serious hackers for hire,red rooms,hit men for hire and serious weapons dealing. Nasty.

Don't go near any of it. The guys that use/make these sites know what they are doing and there are countless tales of people gaining access without the slightest idea what they are doing and regretting it badly.

Thanks.
So Ron, does any of that lot match what's on your shopping list for today?!

In my previous life as a forensic computer examiner a lot of my work came from the so called 'dark web'. A paedophiles playground and if you use it you better have a good reason if you ever have a run in with the authorities, especially law enforcement.

Chris has summarised it well and it's not IMO something the general public should be using, unless they what to hide what they are doing.

Even the worst, most despicable hi-fi forum out there are like a bunch of fluffy bunnies compared with what you'll find in the dark web.  Don't do it!

As has already been pointed out the Dark web and the Deep Web are two different things.
the Deep Web gives you access to lots of the stuff that the search engine do not list in their general rankings. This can be academic papers, etc. A good place with useful info and links is deep-web.org/how-to-research/deep-web-search-engines
The now defunct Copernic search engine was IMHO the best way to search the Deep Web. I used it for years and was heartbroken when they closed down their servers. A lot of technical stuff can only be accessed via the Deep Web.

Me too, I liked it for indexing servers. However, it's all built-in to Windows now.