Run the installer for Xcode if you haven't done that already.
Since you are just starting out I am going to assume that you are either in a class or have some book to learn from. Most people start with command line programs. Here's how you get one setup.
Run Xcode. /Developer/Applications/Xcode
Create a new project. File / New Project
Create a standard command line project. Open the Command Line Utility triangle and select Standard Tool.
Give your project a name and place to be saved to.
That's it. You are now ready to edit the main.c file.
Depends which version documentation you are looking at . Obviously the old tutorials will be based on IB 2 but there is new documentation included with Xcode 3 for all the new tools.
If you have bootcamp or parallels, and have Windows installed, you could download Visual C/C++ Express for free and compile on the Windows side though.
when u r done writing code, do Build and then goto Terminal of Mac and goto the path where u created this file then do this
bash>g++ filename.c
it will compile, if the output is on console
bash>./a.out