Adding a banner to the sidebar of TwentyTen is as simple as dragging a widget, if you have the code to insert already prepared for you.
This is usually the case with affiliate programs, but let’s go through the steps anyway.
1. First log into WordPress with an administrator account.
2. Select “Widgets” from the “Appearance” section of the toolbar.
3. Drag the “Text” widget onto the primary or secondary widget areas.
4. Paste the HTML code provided by the affiliate system into the large field.
5. Click on “Save”.
6. The banner should now appear in the sidebar.