When you want to send an individual e-mail for things like registration, course completion, etc. I suggest you develop an email class or use one of the many free mail classes that are available on the web. Then, in your registration and course completion script, you build the message and send it to the individual email address.
When you are thinking about the automated sending of things like newsletters, announcements, etc. you need some sort of mailing system where your members/users can (online) subscribe to or unsubscribe from. The latter usually is a database (such as MySQL) driven system. In that db you then keep the user's e-mail addresses and their subscriptions.
In both cases you need a server from where you are allowed to send out e-mails. You can ask your provider.
Is that enough to get you started or do you need more information on any of the above solutions?
Ronald