The distribution files for Solaris and some of the other ones, are in compressed tar format, having the ending .tar.gz . To unpack them, you need gzip and tar. Change to the directory where you want to install Mahogany, e.g to /usr or /opt or /usr/local and issue the following command:
gzip -dc < thedistributionfile | tar xvof -Where thedistributionfile is the complete path to the file you downloaded. You will need to have proper write access to the directory where you install it and tar should show you a list of all files being installed as it unpacks them.