If you have/want wifi, your modem should connect to the router with the generally yellow ethernet cable, then you can directly connect to the router with whatever ethernet cable you got. Most modems only ship with 1 port for ease of installation and troubleshooting so router -> modem -> access to the net is the way it''ll/should go
oh and any wifi fags like me, Check to see if your router supports dual broadband setups. This allows 2.4Ghz (standard wifi, most older and or mobile devices will support this 100% of the time) and 5ghz networks which are the speedy speed boys that other wifi users try to be on. Lower(est?) latency you can get via wifi, not interfered with by rando shit being used in the house, and few devices (or people) support it so you can be the only one on the network and pretend you have the nice blue cable hookup.