Port forwarding is the process of routing network data to the correct port.
A port is similar to a connection between devices. A firewall installed in your system makes use of port forwarding to direct data into a particular port.
Port forwarding can sometimes increase your network speed. For example, say you are playing an online game and if you port forward to the correct port according to the MODEM which you have, to the require port you can have a very fast performance, in playing that game.
Similar things can be expected to happen in case of downloading data, viewing WebPages etc. As we have earlier discussed a firewall is a layer for a computer. It will not allow anyone to go out or to come in to that layer. So, you will not be able to connect to the internet. So when you want to send data you can setup Port forwarding.
For setting up port forwarding to speed up the existing connections, separate settings are available based on various modems, for various activities like gaming, downloading, streaming etc.
Some examples are,
When you upload files it may take port 23.
WebPages are generally assigned a port no 80.