Well shit. You need a few things.
VPN for anonymity, there are hundreds of different ones available for similar prices, you can look up reviews for those. Probably around $10 a month.
You need TOR browser to browse anonymously and connect to these sites. Totally free
You need a bitcoin wallet, most people use Electrum. Also free
Some kind of PGP codec, GNUPG is popular, and free.
Setting up TOR Electrum and GNUPG is easy if you google it.
Basically you need to buy bitcoin and transfer it to your wallet, if you have a job and you're buying recreationally you can buy it online from dozens of websites. If you're into entrepreneurship I'd suggest buying it with cash to remove a trail. localbitcoins.com has a section where you can set up a cash transaction.
You get the bitcoin, put it in your bitcoin wallet, and run it through a bitcoin mixer - a lot of people use bitblender. Then you send the bitcoin from the mixer into the account on the website and use it to buy stuff. A huge mistake people make here is keeping the bitcoin in the original "wallet" it is stored in, which is tied to the website, and sending it through a mixer straight to the site. People have been getting fucked over by legitimate sites having downtime, rendering the coins inaccessible along with other bullshit like that.
Always keep it in your personal account.
As you can see on /r/Dream_Market , dark net sites sometimes scam people's bitcoin stored on their on-site accounts. The other part of this is that if a site gets shut down, the coins are gone. I lost money on AlphaBay when it got rekt, but since I was putting near-exact amounts of money on, I lost about $30 on an account with $10000+ in transactions, which is pretty slick if you ask me.
When you order, make sure it's an address that you have legal access to - don't send it down the street and jack it from your neighbor. A friend's house or yours will work fine unless you're some kind of pablo escobar type, then you'll need a trap house but I doubt that'll apply. When you put in the info, use the real info. Fake names on a real address draws suspicion and makes it significantly more likely that the package will receive attention. 350+ orders in, I've never had a lost or seized package.
The most complicated part of this is definitely the PGP but once you figure it out it's really easy.
I would recommend saving login info somewhere physical, like on a random page of a book, or something similar. You can also put it on a micro SD and hide that somewhere, but that isn't foolproof. I transitioned to paper when my micro SD became corrupted. Luckily I was able to recover the important stuff but I doubt I'd get away with that twice.
If you're curious about anything else, I can help you out.