NVchooser.sh is a bash shell script. There are two ways to execute it.
1) Open up an xterm (terminal window), change to the directory where you downloaded it (probably your home directory), and type 'sh NVchooser.sh'.
2) Open up an xterm, change to the directory where you downloaded it, type 'chmod +x NVchooser.sh' to make it executable, and type './NVchooser.sh'.
I recommend solution#1 until you're more familiar with Linux.