1) You need to unpack the packet you downloaded. You can do it with archive manager. You can also do it from command line - since the linux packet available for download from Second Life looks like a tar-bzip2 archive, the command to unpack it is:
tar -xjvf SecondLife-i686-18.104.22.168167.tar.bz2
That will create a directory where all the files are unpacked.
2) You may perform an installation by running the
install.sh within the unpacked directory. But it seems that just running the application will do this automatically, so this isn't required.
3) You can run the application directly by running the binary file
secondlife in the unpacked directory. To do this from command line, enter the directory and just run
Also note that in the
README-linux.txt file of the package it says
For in-world MOVIE and MUSIC PLAYBACK, you will need (32-bit) GStreamer 0.10
installed on your system. This is optional - it is not required for general
Hope this helps!