How to learn developer logic?

Hey guys,

First off I'm a design agency founder, I completely love great and beautiful design you can find us here But my real dream is to be able to not only design the apps but actually build them. I constantly like to drip my feet into development and have gotten pretty well versed in HTML, CSS, and even react native to build the front-end. Meaning I can put together enough code to show the design, But when it comes to adding the business logic I have no idea what code to implement or even what is available to me to implement. I went through most courses on Codeacademy but I feel like I need to know why something works before I can use it. And Codeacademy just spoons feeds you a solution. Is there books to read to understand the logic behind solutions? Are there courses or video to learn from? My main goal is mobile app development. Mainly react native. Any thoughts would help.