From the Apple Menu, select System Preferences.

Click on the Network icon.

In the Show: drop down menu, choose the device you wish to configure (dial up, airport ethernet).

Click the Proxies tab.

In the Select a Proxy to Configure window, choose Automatic Proxy Configuration (you may have to scroll down to see it).

Click on the check box next to it to make Automatic Proxy Configuration active.

In the URL: window, type http://copy.its.yale.edu:8080.

Click Apply.

Proxy Configuration is now complete. To test, open Safari and go to a Library proxy-restricted page. You should see the following screen: