Source tarballs are packaged as bzipped tarballs. To unpack a tarball from a unix-like shell (or the cygwin shell), type:
tar -xjf <source-file.tar.bz2>
Note for Windows users: using WinRAR to unpack source archives will not work. The archive contains zero-length files which are not unpacked properly. For windows, use for example 7 zip software.