New user

Good morning, my house has never had cable we were satellite only. Cable wasn't available at the time. When it was we had internet only hooked up. Now I'm trying to hook up X1. The cable comes through the wall and to the router/modem only. There is only one male coaxial connector on the router/modem so do I need a splitter? What's the best one? Do I get it from Comcast?