Most of the time, people will subscribe to your autoresponders by completing forms on your web site. At its simplest, a subscription form simply asks your contact to enter their email address and click a button.
You can also ask for more information on your form, first name, last name, full name and any number of custom fields (explained later). Here is an example subscription form:
It is a good idea to at least ask for your contact's first name so that you can personalize your messages to your new subscriber with the {FIRSTNAME <default>} tag.