If you add users manually, and you use the option to 'Generate password and notify user', an email will be sent to the new user.
If you would like to customise/edit the email, then:
- go to Administration> Site administration> Language> Language customisation
- Choose English from the drop down
- Click on 'Open language pack for editing' (then wait...)
- Click 'Continue'
- click on 'moodle.php'
- put 'newpasswordtext' in the field for 'String identifier'
- Click on 'Show strings'
- Copy the text in the 'Standard text' box and paste it into the 'Local customisation' box (do NOT include the 'string contains a placeholder' at the end)
- Make the changes required to the text in the 'Local customisation' box
- Click on 'Save changes to the language pack'
- Test your changes
Moodle will use the text in the 'Local customisation' box.