How do I get started?

I have played tons of RPGs with a ridiculous amount of hours in most of them. I am heavily into DND and building storylines and making maps and world building when I DM.

Basically I want to make my very first game and I found this place! Is RPag maker a subscription or something I pay for once? Also after I buy it how easily can it be customized? I apologize if these questions have already been asked, just putting out feelers while doing my own looking.