I would have to ask you if your looking to replace your existing Wi-Fi service from your MAIN Modem, and use the this one in its place to play games, stream movies ,etc.?
If that is the case, then yes you can certainly plug this into your main modem, and then follow the easy directions to set it up and your ready. I would certainly advise that you get into your main modem function settings and disable it's Wi-Fi- to eliminate any possibility of interference.
Hope this helps.
JKL