footer showing up in side bar

What theme are you using? Where did you download it from?
Have you tried validating your site’s content?

My site is based on the “Thematic” theme, downloaded from WordPress. I have not tried validating anything – my initial search into this produced confusing results. Could you explain briefly how I go about validating the content?
Thanks very much

Try using the W3C validators:
HTML – https://validator.w3.org/
CSS – https://jigsaw.w3.org/css-validator/