How the hell do I pay for something with bitcoin?

Let’s just say that I’m not able to get a certain pharmaceutical drug in my country and so have to buy on the online black market. The “service” used to just accept bank transfer but now only accept bit coin. Crypto is something I know NOTHING about, for years I’ve tried to understand it (purely out of interest) and my brain will just not allow anything to absorb.

Now my mental health depends on it, is there anyone that can give me an easy step by step guide on how I pay with bit coin?

Apparently I need some “wallet” app. Which one? I don’t want to trade/buy/sell crypto. I just want to make a monthly purchase each month of around £60. How do I get money from my bank account changed to bitcoin??? How do I send it?? Argh!! It’s so confusing!

Please help

(I’ve watched plenty of YouTube videos and they just still don’t make sense)

EDIT - this is a trusted person/business I’ve been using for years who have just recently changed to bitcoin for some reason. There is no scam involved. ALSO, it’s not the dark web, it’s the black market - 2 very different things