I have few sales and I don't understand how I can make money with my software.
Making money on your own with software is basically starting a business on your own. Most people do not operate their own business. They work for someone else.
To sell sofware, you need to make something that people would buy. But chances are, that someone else already made a software capable of doing what your software could do . And if we talk about games, well, there are about 900k games on itch and the vast majority of them are unknown and do not make money.
Small software companies usually do contract work. That means, they have someone willing to pay them to create a software. It is more of a craft thing. Like hireing a painter to paint your house.
But on itch, this is the other way around. You make the software (a game), and try to find people wanting to play it. This is hard.