To permit and direct incoming traffic from the Internet to a specific computer and/or servers inside your internal network with a specific service, you have to define an object that will represent the Server.

1. Log into the appliance Web interface (GUI).
   
   
2. Go to 'Access Policy' - 'Servers'.
   
3. Click 'New'. The wizard window should appear.
   
4. Select the server type that you want to define. There are 5 common built-in server types: Mail, DNS, Web Server, FTP, and Citrix Server. If you want to create a custom server, you should choose the "Other server" option.
   
   
5. Give the server object a name and the internal IP address.
   
6. Select the zones where the server will be accessible, this will create the policy rule. 
   
7. Select the NAT option. 

If you are trying to create a port forward, enter the port the firewall is listening to on this page and the port the server is actually listening on the first page of the wizard.

Note the Advanced option, "Force translated traffic to return to the gateway". This option will cause the NAT rule to change the source to the gateway IP after passing traffic to the server. 

For more information, refer to "Defining Server Objects" in the relevant appliance Administration Guide.