Open Safari, then go to Preferences.
In the Advanced tab, click on Proxies then Change Settings.
Check Web proxy (HTTP) and Secure Web Proxy (HTTPS).
In the Web Proxy Server field, type the IP address (1.2.3.4) and Port (8800, 3128, 52931 or 80).
Click Ok.
Click Apply.
Next, open a browser to ip-check.net to verify that the IP displayed is the proxy's IP address.
If so, you have successfully proxied your internet connection.