AppDelegate.h and AppDelegate.m

Can someone clarify somethings for me regarding AppDelegate.h and AppDelegate.m ?

Do you declare and define your classed in both of these files collectively ?

Are all my class declarations in one .h file and defined in the other .m file ?

I’m trying to follow through the Objective-C Programming 2nd edition and I’m stuck on some of the wording. Since I’m using a newer version of Xcode I’m finding that things aren’t 100% while I’m trying to Work alongside some of the examples.