If you want to understand how…

If you want to understand how to bridge the gap between the REST API and the Customizer, Weston Ruter has you covered. With an incredibly detailed blog post and a sample plugin, you can get started taking advantage of manipulating data using the API, through the Customizer interface. This shows a lot of what is possible in a rapidly evolving Customizer, and his writeup and code are an excellent way to learn.