tar.gz files are a compressed bundle of one or more files. These files can be anything, that a filesystem can handle. It is quite similar to the concept of ZIP files on Windows (and other systems).
Whatever data is contained in a compressed archive (be it tar.gz, zip, bz2 or whatever) has to be uncompressed before you can use it.
When uncompressed, figure out what kind of files these are - executables, installers, README, etc.
The Archive Manager is a handy tool that allows you view the contents of an archive file, without unpacking it.