Objective C and C++ are both Object Oriented extensions to the Procedural C programming language. You can access the Carbon API using simple C data structures and methods. You can then wrap the Carbon function calls into neat C++ objects. Metrowerks has a C++ library for MacOSX called Powerplant(?).
The Cocoa Interface is written in both Java and Objective C but is much cleaner than Carbon. Carbon is a bridge between Classic and X so the Old world companies didn't have to start from scratch.
Interface builder allows you to add visual interfaces to your apps and connect them to methods for handling actions and objects for handling data values. It is a visual way to create widgets and their corresponding objects.