BulkMail has a feature to allow you to create pages in your account. You could use a page as a landing page for potential customers to sign up to your newsletter. You could also use a page to link existing contacts to so they can change what lists they are subscribed to depending on their interests. You can create pages for notifications that your contacts would receive like if they unsubscribe, if they fill in a form etc.
The difference of a page compared to an email is that an email is sent to a contacts inbox whereas a page is linked to from an email. The page would open in an internet browser and could have a form embedded into it or just a message if they unsubscribe.
BulkMail has default pages that will be sent in the case that you do not have any pages set up for these types of action. What creating your own page does is it allows you to create branded pages instead of the generic default pages that BulkMail generates.
If you include a send to friend link in your emails so that your contacts can forward your emails, It is recommended that you create your own customised pages for this so that the process is consistent with the branding and style of the email that the send to friend link was attached to.