Just create a file named “functions.php”, place it into your theme folder and put the following code into it
<?php
if ( function_exists('register_sidebar') )
register_sidebar();
?>
And this into your sidebar.php. Example:
<ul id="sidebar">
<?php if ( !function_exists('dynamic_sidebar')
|| !dynamic_sidebar() ) : ?>
<li...
A link to the theme would be helpful.
Failing that, the best we can do is point you to here:
http://automattic.com/code/widgets/themes/
That has full instructions on how to do it.