Port Forwarding Help

Hello,

I'm looking to port foward so that I can use my Desktop for for applications that utilize TCP/UCP. The desktop is connected by ethernet to a Netgear R7000 NightHawk Router which I purchased and a Cisco DPC3939B Gateway which was provided to me. My question is will I need to portforward both devices or just my gateway or router and what IP should I use? As this is my first time into this subject any other advice is greatly appreciated!