Can't hook up cable box to my new Vizio VHD32M-0807. HELP!

I just unboxed a VHD32M-0807 and I'm trying to connect my cable box to it. I had a previously old Apex that finally went out on me. But when I turned the Vizio around there is only one plug. I tried to unscrew the cord from my big Apex to plug into the lone "antenna" outlet in the back but the cord is so thick it won't let me plug it in. What am I missing? Thanks in advance.