Depending on how you obtained the CDT, you might have also received a toolchain with a built-in CDT integration. However, if you downloaded the CDT from the Eclipse repository, then you will require a toolchain before you can build and debug any projects.
The standard CDT supports integration with the GNU toolchain. This includes GNU's make, gcc compiler, and gdb debugger utilities. If you require a toolchain to build software for your development host, this is the best choice to get started.
Each platform that runs the CDT requires different steps to acquire this toolchain.
For windows, MinGW and Cygwin are the two main platform choices for acquiring the GNU toolchain. It is important to understand the difference between them. Cygwin produces executables that use the Cygwin POSIX runtime. Note that this runtime is GPL licensed. MinGW produces native Windows executables that do not require a separate runtime.
For MinGW, the recommended method to get the toolchain is to install it from the Wascana project at Eclipse Labs, http://www.eclipselabs.org/p/wascana. Wascana includes the MinGW toolchain as well as a number of open source libraries that can be used for Windows development. See the Wascana site for installation instructions.
As an alternative, the MinGW site itself, http://www.mingw.org also has an installer. The CDT will find that install if it is placed in the default C:\MinGW directory.
Cygwin can be install from the Cygwin site at http://www.cygwin.com. You need to manually select the gcc, gdb, and make packages to install the toolchain.
All Linux distributions include the GNU toolchain. They may not, however, be installed by default. For instructions about installing the GNU toolchain for Linux, see the instructions for your particular distribution.
The GNU toolchain is supported on all platforms that the CDT supports. For instructions about installing the GNU toolchain on your platform, see your platform vendor.