1) Make an advanced theme described here:
http://www.question2answer.org/advanced.php
No worry, its kind of very easy.
2) Add this function to Your new qa-theme.php
function footer()
{
$this->output('<DIV CLASS="qa-footer">');
$this->nav('footer');
$this->attribution();
$this->footer_clear();
$this->output('</DIV> <!-- END qa-footer -->', '');
}
3) Add to Your function as You desire:
Example adding a text in a new div:
$this->output('<DIV CLASS="my-new-footer-class">');
$this->output('<p>My new footer text.</p>');
$this->output('</DIV>');
If You need more help, let the community know about.
Please do not change the qa-theme-base.php, Instead use allways Your advanced theme, as You can allways just change back to the standard theme without any losses.