I made quite a lengthy post on this a few weeks ago. Here's a cut and paste of it.
It's easy to access [the dark web] using the tor brower (and impossible to access without the tor browser). Just download that, and take it from there. Names of sites only accessible via tor end in .onion. (Using tor you can also access ordinary sites too.) Ordinary search engines don't index the dark web, and to find anything you need to use one of the specialized tor search engines. (To get started, just do an ordinary search in google to find the .onion site names of a few dark web search engines.) However, it's not easy to search the dark web effectively, because the search engines are not very good (nowhere near as good as google), and many of the links they suggest no longer work. My advice would be that tor is more trouble that it's worth, unless what you are seeking can not be found on ordinary websites. It is difficult for your activities on the dark web to be tracked, but if you are doing anything nefarious remember that it is not completely impossible. (You may wish to disable javascript on your machine before you use the dark web. That may mean that some dark web sites won't work, but it also prevents a malicious script from finding out the IP address of your machine - which of course can easily be traced to you - and reportng it to someone you don't want it reported to.) Also remember that if you pay for anything by credit card on the dark web, you lose any possibility of privacy. Bitcoin, or something similar, is much safer, though even that can sometimes be traced back to you. (Using a bitcoin mixing service makes it harder to trace.) If you are planning on doing anything nefarious. and have some IT technical skills, it is much better to run the tor browser from a volatile operating system, such as tails, rather than from your usual operating system. (I understand that Windows 10 has a bad habit of reporting back to Microsoft every single keystroke you make.)