What are the basics of iOS design development?

Question

iOS

I am engaged in web design, but little by little I began to look at mobile applications, who can tell or give a link to the technical basics of design development for iOS, for example, such as:
I made a design for iPhone 6, but what about previous versions (screen sizes) what is required from designer in such nuances? Indents from the edges of the screen, etc. in general, the essence, I think you understand what I want to get acquainted with)

Answer 1

It's probably worth starting with this https://developer.apple.com/design/

Answer 2

Still wondering what font to use?