ELI5: How do I sell software?

I've been learning a bunch of programming languages this year, and I'm starting to make a desktop application for recording sound (specific to a particular profession).

Before I sink a load of time into this project, I'm wondering how I would go abouts selling the software. I'm getting really confused with licensing; both the best way to distribute software and prevent pirating, as well as what I'm allowed to sell.

I'm using Qt Designer to create the UI and I think I have to buy a very expensive business license to sell my software legally.

I'm considering having a web server with license keys for authentication, but users of the application might not always be online. I'm also scared I'll overlook something and the first hobbyist hacker that comes along will have my software hacked in no time.

Are there any guides on how to sell software as an individual? Googling is unfortunately not giving me very relevant results.