There are many events which trigger an e-mail from Magento to your customer:
When the customer places an order, Magento sends a confirmation e-mail.
When someone creates an account on your site, Magento sends a welcome e-mail.
When you update an order in Magento with shipping information, Magento sends the customer a shipping update, and many more.
Note
All of these e-mails must be customized for your store! In the default Magento installation, these e-mails use "Magento Demo Store" as the name of the store. They use (800) DEMO-STORE as the phone number of the store. And, they include e-mail addresses that point to the makers of Magento. If you don't customize these e-mails, then you will be sending confusing and possibly embarrassing messages to your customers.
There are two ways to customize these e-mails. One way is to edit the template files that are supplied with Magento. You can find directions on how to do this on the Web. However, if you just edit the...