Can I put a BACK button in my HTML page?The short answer: "no." The user is well aware of the "back" button in their web browser and will use it when appropriate.
The long answer: if you are writing a CGI program, you may be able to take advantage of the HTTP_REFERER environment variable, which sometimes contains the URL of the page the user came from. This information is intended to help you discover which pages link to your own. However, there is no guarantee that HTTP_REFERER will be set, or that it will be set to the immediately previous page. Also, if the user follows such a link, the real "back" button will not behave as the user might reasonably expect afterwards. Under most circumstances, you are best off exhorting the user to "back up to the previous page." All web browsers offer such a feature.
World Wide Web FAQ