How to Direct a Port From My Modem To My Router?

So I'm trying to make a minecraft server, but I have a modem and a router. I have an xfinity modem and a Netgear Nighthawk X6. I used to be able to port forward on the modem, but now I can't port forward at all, on the router or the modem, it is not firewall issues. So I did some research, and I found this page: http://www.minecraftforum.net/...dem-router

Apparently he found a soulution, but I do not understand it. If anyone can help me on this, it would be greatly appreciated… I had to go into my modem's firmware, and direct the port over to the router, from there, the port had to be directed towards the PC. Works perfectly. WHAT DOES THAT MEAN!

Added (1). Also sorry for double posting, I didn't know that you could add details.

Guest

If your modem has a section for pooort forwarding, that means it is a router as well. All port forwarding does is forward the packet for that port to the next device up the chain, nothing more. Thus, modem must port forward to the IP address (WAN/Internet) of the second router. That is all your modem can do.
Then, your second router will get that same packet, and has to be instructed to port forard anything with that port on its WAN port, to another port (LAN/PC) port.
And so on. All port forwarding does is pass on the network packet with that port to the next device.

Adrian