This policy allows you to control printing from remote machines. You have the option to Allow all printers… except ones you specify, or to block all printers except those that you list.
To add printers to the exclusion list, click on the ‘Add…’ button. This will bring up the following dialog box, which lists all printers available on the network:
You can then select the printer(s) you wish to allow/block, and click on ‘OK’. Alternatively, you can block access to all printers, except … and use wildcards to specify the printers you wish to block.