Please refer to the releases web page for information on how to obtain GCC.
The source distribution includes the C, C++, Objective-C, Fortran, and Ada (in the case of GCC 3.1 and later) compilers, as well as runtime libraries for C++, Objective-C, and Fortran. For previous versions these were downloadable as separate components such as the core GCC distribution, which included the C language front end and shared components, and language-specific distributions including the language front end and the language runtime (where appropriate).
If you also intend to build binutils (either to upgrade an existing installation or for use in place of the corresponding tools of your OS), unpack the binutils distribution either in the same directory or a separate one. In the latter case, add symbolic links to any components of the binutils you intend to build alongside the compiler (bfd, binutils, gas, gprof, ld, opcodes, ...) to the directory containing the GCC sources.
Likewise the GMP, MPFR and MPC libraries can be automatically built together with GCC. You may simply run the contrib/download_prerequisites script in the GCC source directory to set up everything. Otherwise unpack the GMP, MPFR and/or MPC source distributions in the directory containing the GCC sources and rename their directories to gmp, mpfr and mpc, respectively (or use symbolic links with the same name).