Please open a browser tab, type: http://192.168.1.1 and log in with the default administrator password and username (admin / admin). Click the NAT menu on the left from Port Forward. In order to open a certain port, please fill the name of the application you want to open port for (it can be any name) the port range, protocol mode (TCP, UDP, both) and the IP-address for (192.168.1.X, where X is the number from your IP address assigned through DHCP).