The quickest way is to hire a private teacher to work with you hands-on. That's also a little spendy.
If you're good at self-motivation, there are thousands of tutorials on various app-building techniques that you can walk through. They exist as articles, videos, interactive projects — there are lots of options.
But the most important part of learning any new skill is to build experience. No amount of preparation or study can stand in for solid hours of real experience. You have to start building to start creating the mental models that are required to conceptualize computer programming. And those are kind of like balance, or juggling: they have to be experienced, not learned.
I have quite a bit of experience building various software applications, so if you'd like help putting together a DIY curriculum, send me a request for a 15-minute call.
I would suggest that you take a look at the courses on Udemy.com They have some very good how to build mobile apps courses. If you are a programmer this should be a great way to get started. You can also look at Chocolate Labs or James Carters BlueCloud courses. You could look at Zapper for a build it yourself without prgramming app system or take a look at Buildbox (they have a monthly subscription but you can only buy it at certain times) for building games.