Iframes short for inline frames are a really great addition to any web-page. First put this code..

<iframe FRAMEBORDER="1" width=80 height=80 src="main2.html" name=COOLFRAME></iframe>

..on the page you want the frame to appear on. Adjust the width and height to fit your personal preference. Then make another page called main2.html or whatever you decide to change the file name too. That is the page that will show up inside your frame. Hope this helped.