Hey, how do I actually start this? I have PAID for the Pico-8 but I cannot see any obvious way to begin. Help anyone?

boot the console, type help, press enter.
hit esc to swap between IDE and terminal

I suggest looking up some beginner tutorials on youtube and make heavy use of the PICO-8 wiki, particularly the API Reference page.

Just keep in mind that you don't need to learn every function right away. Some games you might only need a few functions and some if/else statements to make. Start with something really simple. When you hit a roadblock, check if any of the other functions might make it easier to do what you're trying to do.

Start here! https://mboffin.itch.io/pico-8-top-down-adventure-game-tutorial

I see you tagged your question "Log in", so maybe let's back up and make sure the preliminaries are out of the way.

Have you downloaded the Pico8 software and installed it on your computer?