how to add widgets?

Hi, I was using the Digg 3 column theme in my wordpress.com site and was hoping to migrate the whole thing to my ww.wp.xz.cn site, but after putting the theme on I can’t seem to be able to add widgets.

There IS a sidebar.php file in the theme editor and I haven’t been able to find any clear instructions on how i can add widgets anywhere.

Please help, anyone?! I want to get my new site up quickly!