Don’t ever feel dumb. Just feel “challenged” and overcome ??
Make sure that your API key is entered into the space provided – without any leading or trailing spaces. Next, you must click the button “Update Configuration”.
Unlike many of the other options, which are set via ajax and do not require a page refresh or submit button, setting the API key requires a full form submission to complete. If you follow these instructions and still have issues, check and make sure that you are using the correct API key (“Key for browser applications” aka “Browser Key”).
If that doesn’t work, let me know what browser/operating system you are using (Microsoft/Mac/Linux) and I will see if we can figure it out together.