Footer BG showing up on the top of my page

You have a number of errors in your code. Fix those and your problem will go away.
https://validator.w3.org/check?uri=http%3A%2F%2Fwww.airportparking.org%2Fhow-to-save-money-on-airport-parking%2F&charset=%28detect+automatically%29&doctype=Inline&group=0

I really don’t know how to fix these errors. Is there a way to find out how to edit my files according to these errors?

A good start may be to place this:
</div>
in your index.php immediately before the call to the footer.