Not OP, but...completely bootstrapping it?
1) Learn the tools to build your product.
2) Research some product / markets, see what other products are out there. Chasing some noble idea, or "hidden gem" just to gain first-move advantage isn't all that, IMO. It's almost always better to join an existing market where proof of concept has already been done for you. Even better if the existing products are stagnant or lacking.
3) Figure out a business and marketing plan, doesn't have to be the most complex thing in the world - but it forces you to do some research before just diving into something blindly.
4) Start developing your MVP. Reach out to users in the relevant places, which means going to forums, twitter, subreddits, etc. Try your best to get user feedback, iterate your product on said feedback. Any money you get from donations, purchases, gifts, family, whatever should go towards infrastructure and marketing.
5) With enough users, look into how you want to monetize your product. Ads? SaaS? Purchases? Lots of ways, but they all have their pros and cons.
But, to be honest, it's a lot of work for a single developer. Especially if you're not already experienced with all the various aspects. You're basically gonna be doing everything on a smaller scale. Lots of things to learn, lots of things that can go wrong.
And importantly, it can take years to build up a userbase large enough to live off the project. Sometimes you never grow to that size, and the product life-cycle has peaked, on its way downwards.
The people that do this kind of stuff, have tried and failed multiple times before. But there's always something to learn, which you'll take to the next project.