hey dread

i used some online guides how to setup tails OS and access dark web here but i feel naked... how can i secure myself more? I use old pc to boot tails from usb and i browsed some markets but there are things on there i don't understand. I've googled PGP but from guides and articles it says only for email? How can i integrate it to security between me and seller? i searched using search button but couldn't find one guide to help me? any ideas?