Messages templates are the templates of the all mails send by your store. At the list page you may find all possible templates, or may even add a new one.
Edit is very easy, just find the template and open it by clicking the name. Similar to action. Below a quick summary of the fields.
Form is very intuitive, what is important and may occur a troubleshot is 'Is active' setting, as if not active the message template can not be send.
At the field email account you may specify which email account will be used to send particular message. You may define different email (for example firstname.lastname@example.org) to send notifications related to purchase, while information about customer actions (registration, password recovery, etc) will use another one (for example email@example.com). First, need to configure email accounts to be able to use this feature. [MORE]
If needed there is a possibility to send message with an delay