A simple script would look like:

#!/bin/sh

echo "Hello, world!"

Where the first line consists of "#!<path to the shell to use - usually
/bin/sh>" and then the rest of the file  consists of the commands to execute  -
basically anything that you can do from the command  line.

Once the file has been saved, execute 'chmod 755 <script_file>' and you will
be able to use your script just like any other program on the system.