When you add Advertisers or Sponsors to your site, they'll show up in the footer by default and look something like this:
Your images will appear in the footer as a grid - this is the Sponsors widget. It will display up to four Advertisers with the images and links you've specified in the Advertising section of your Site Settings.
You can change where this appears or remove it entirely by editing the arrangement of Widgets under the Appearance menu.
You can change the title of this section and use it for anything that you would like where you upload an image and can link to another site.