How do you make new software like Bill Gates and Steve Jobs?

These guys didn't just build "software", they created operating systems which is one of the pinnacles of computer science & engineering. Furthermore, both were innovators in a time when pcs weren't really a thing for the masses, excessively limited & expensive technology - my father purchased his first ibm for $10k of the day.
Nevertheless, everybody starts at the bottom. You need to take a course in programming. Online lessons are okay, but it's better if you have some experienced programmer pointing out style errors along the way - how you write makes 50% of the difference in quality, beside algorithms and ingenuity. Once you've got a handle on coding, you can write basic software - it's a matter of practice and knowing your goals. For the more advanced kinds, and to be able to write anything professionally, you need degree level educations - either in computer science (software) or engineering (hardware) or a combination thereof, whither your preferences wander.
And fyi, jobs was never a programmer. Wozniak was the tech genius who built the apple I, additional kids hired along the way, it's in the movie(s).