Ethernet to CoAxel

Hi, I am as newcomer to comcast, and I have seen that I may need a coaxel socket in my house, but unfortunately I do not have one. I was wondering if maybe comcast would allow me to use an ethernet to coaxel adapter. Ex. Connect my ethernet cable to my ethernet jack on my wall, then on the other end, connect the cord onto the ethernet coaxel adapter, then connecting it to my modem? If so I was also wondering if I could use one of my friends used modems rather than buying one from comcast itself. I appreciate any help I can get!