How to use private proxies or shared proxies with Mac
Choose Apple menu > System Preferences, and then click Network.
Choose the network service you use from the list, for example, AirPort or Ethernet.
Click Advanced, and then click Proxies.
If you configure your proxy server settings automatically, select Auto Proxy Discovery to automatically discover proxy servers, or select Automatic Proxy Configuration if you are using an automatic proxy configuration (PAC) file. If you select Automatic Proxy Configuration, enter the address of the PAC file in the URL field, or click Choose File to locate the PAC file.
If you configure your proxy settings manually, do the following:
Select a proxy server, such as FTP Proxy, and then type its address and port number in the fields on the right.Select the “Proxy server requires password” check box. Enter your account name and password in the User name and Password fields.