Once you have the notification system in GLPI configured and running, you could run into a common beginner issue where the URL of the ticket field is shown empty.
It is ##ticket.url## tag in notification template, usually formatted with its description field:
##lang.ticket.url## : ##ticket.url##
The fix is easy, just navigate, logged in with Super-Admin account, to Setup - General - URL of the application and fill it with your actual URL.