Hook the cable to your VCR then use RCA connections from your VCR to the plasma.
Read The Manual that came with your plasma that should specifically show you how to hook up stuff to the plasma as well. It should be pretty detailed, most are.
Finally: CALL YOUR LOCAL CABLE COMPANY: Get a set top box with HDTV if at all possible. What will come out of your VCR will look really bad on your display, simple as that. Regular analog cable is not very pretty when you view it on most plasmas. Watchable, but not the same as HD by a long shot. When you get the set top box (STB) from your cable company, hook it up component video or DVI/HDMI cable.
