For those who want a more comprehensive guide the Dark Net Market Buyer's bible is a great resource:
http://biblemeowimkh3utujmhm6oh2oeb3ubjw2lpgeq3lahrfr2l6ev6zgyd.onion/
It can also be found on tor.taxi:
https://tor.taxi/ which is accessible via the clear net in case anyone doesn't trust this onion link (always good to double check/verify any links as there are many phishing sites).
All you need to access it is download tor browser and access the link via tor. The link won't bring you anywhere if you access it through a regular browser.
@DeepDespair101 Would you consider adding this to the OP?
Tor.taxi also has a monero guide. 99% of vendors of the dark net have switched to monero as it is a
true anonymous cryptocurrency unlike bitcoin. My advice is to skip bitcoin and just find a crypto exchange that will sell monero directly.