Verified answer

Objective C is a programming language, XCode is used to write code, and Cocoa is a framework used to develop applications.

In a Software development environment there are various components for the development process. In the Mac World:

Objective C is the programming language

XCode is the IDE or Integrated development environment

Cocoa is a specific library typically used for MAC/ IOS based projects

Yes you will be using all 3 if you are interested in IPhone Development :)