GD Affiliate Center has many ways for adding one or more ads into the website. Most likely easiest way to do it, is by using the widget called Ads Block. With this widget you can set number of ads, size and affiliates to include.
Widget is very easy to set up, and you can start by setting who will be able to see the ads. Display to option allows you to show ads to visitors only, and hide it from logged in users. If you don’t set title, widget will render without heading element.
You need to select ads format (size), affiliates to include and how many ads to show. When you do that, you can add some extra markup elements to add before and after each add, and before and after whole block of ads. The screenshot with settings on the right is exact widget settings used on Dev4Press for Blog sidebar to display 4 ads to visitors with size 125×125 pixels.