When people speak of autoresponders, they may mean different things. There are really two types of autoresponders. The first is a thank you message in response to filling something out and the second is an email address which, when it receives a message, automatically responds with a message of it's own.
A very important datum to remember when creating your web site is that you want your visitors to come back. It doesn't matter what your site is about, if people stop by but never come back then you are missing out on some very important opportunities. At the very least, a lack of return visitors says your site is either not changing or has nothing new to offer.
There are many ways to generate return traffic. Of course, the first things that must be true is your site has (a) good content, (b) offer something that people want to know, have or buy, and (c) is dynamic (changing). If your site is static (finished) then you ca expect people to stop by once or twice and then never come back. There are too many other places on the web where they can go to get a new thrill.
A very good method to use to get return traffic is to get people to give you their email addresses. Before I go any further on this topic I will give you a note of caution: DO NOT SPAM and DO NOT EVEN ATTEMPT TO AUTOMATICALLY CAPTURE PEOPLE'S EMAIL ADDRESSES from your web pages.
So how do you get people to send you their email address? By offering services which require or request them to do so. One way is to ask your visitors to send an email to get more information. This is a true autoresponder and there are many companies that will provide this service to you. Another method is to include several forms to fill out on your web site, which you follow up with a thank you or confirmation email to the person who filled it out.