So step zero consist on acquiring your first customer/user. This is usually when having a non-tech co-founder or someone who's good at selling would make a huge difference. We always bypass this step of acquiring the first customers, it's only when you build something and ship it that you hit a wall. You will not rank in google at first, no one will ever mention your name and the only queries you'll get on your SaaS or whatever product you have will come from your own IP. That's what I'm talking about. You just launched, now what?
So you need to go out there and "manually" pitch your product to people. Introduce yourself, tell your story, prove people what you've built is what they want. You would usually fail capturing the needs at first because of a lack of interaction with your targeted users, you will build something that isn't exactly what they want. So you need to quickly adapt to that early feedback, which is why going out there and trying out your MVP or prototype very quickly is a key to success. This is what I mean by "people need to see real faces". You could pitch your product to your mom, friends, potential users, potential partners who could help you move to the next step, etc.
The best way to find out "how to found a company as a single founder" is to give it a shot. You'll basically collect all the answers to your question.