Xcode 2.5 is the version for Tiger. This will install the Xcode IDE and GCC for compiling C, C++ and Objective-C. Interface Builder is included for Cocoa/GUI apps. There are also older versions of Java and Python/MacPython for building Mac-looking apps/applets.
All of the documentation is included in the /Developer/ADC Reference Library/ folder, but I would recommend getting started with a dedicated Objective-C or Cocoa programming book.
If you want something easier to start with, try RealBasic v5.5.5 (Available from the
PPCAppStore). This is a quick way of learning the ropes with drag and drop interface building and a VisualBasic-like language for scripting communicating between UI objects. RealBasic 5.x will compile Carbon apps for both Mac OS X and Mac OS 9. If you like the simplicity of the language, you can continue using RB skills in modern app development with
Xojo, for "Rapid development" of macOS, iOS, Windows, Linux and Android apps.
If you want a really obscure challenge and would like to write apps and drivers for Mac OS 9 in Pascal, C or C++, download
MPW GM 3.5 (
made free by Apple) and/or CodeWarrior (v7.1). With enough googling and archeological digging through old software archives, you will find the software, documentation and useful sample programs to get you started.