Script start on boot: where to find messages

Question

I would start a script on boot for Raspberry with raspbian. I found and followed well known method to start script on boot. But, where can I find the messages of my script? I'm not sure that the script started. For example, a simple script:

#!/bin/bash
case "$1" in
start)
   echo "Start script"
   ;;
....
esac

exit 0

Where can I find the "Start script" message? Thank you!

Roberto