Cocoa based apps are not really for the beginner. If you are serious about learning to develop Mac based apps, the usual syllabus is as follows.
The C language, then...
Objective-C, then finally...
Cocoa
Each builds on the other. But, starting off as a beginner with Cocoa is like trying to learn how to fly in a 747 rather than a Cessna 150. That would be very tough.
Almost all current languages (except for some old ones like Fortran, Basic and Pascal) derive from C. If you get some C experience, you can move up to the others just by buying a book. Java, Perl, Python, Ruby, etc are all C centric.
All you need to start with, is a good beginners C book. The compiler is already on your Mac. There are lots of C tutorials on the 'Net, but I have always liked a real book that I can sit down with in a quiet place and get off the keyboard for a while.
Go for it. I started almost 35 years ago with interpreted basic
(all that was available in 1975) and a 2mhz machine with 24k of ram. Programming has been my hobby ever since.
Konan