tar.gz is a linux compression/archive format. If you are running KDE, you can typically open up konqueror (the kde file manager), right click, and select to unarchive/uncompress. It will likely create a subdirectory, possibly by the same name "orinoco-015rc2". Navigate to that subdirectory, and look for a "README.txt" file or a "INSTALL.txt" file.

The above is a standard "convention" for tarballs (affectionate name for "tar.gz" files). Unfortunately, not everyone follows the convention.