Please go to http://doc.tiki.org for documentation on how to use Tiki
Email notifications can be used to notify some email addresses when an event occurs in a Tiki site, you have to be admin to edit email notifications.
Enter the email notifications screen following the "email notifications link" from the admin section of the application menu.
You can enter as many addresses as you want for a specific event and remove addresses that you don't want to be notified.
So you want to customize the mail that tiki sends when some event occurs, you can do this by simply editing a template from the edit-templates screen or using a regular text editor.
You will see how the email is constructed at the template and you can edit the text and the formatting as you need. The whole mail message is 100% configurable.