the most secure possible? you'll need to learn a ton. you'll get there, but it'll take a while.

decently secure? install Linux Mint, install your updates, don't run sketchy commands with URLs in them unless you know what you're doing, maybe follow a hardening guide. you'll be okay.

if you need to be extremely secure and private, install Tails on a USB stick. it will be slow and frustrating, and you'll need to save files to a second USB drive, but it will probably keep you pretty safe, and it's decently user-friendly. just make sure you keep Tails updated! you'll have to do that by flashing the new Tails onto a new USB drive, there's no easy way around that.

those are your two most user-friendly, safe approaches.