Never consider yourself dumb just because you are working to learn something new to you.
Something like this from Office Depot:
RF Modulatorbut Wal-Mart and others carry similar devices. I was always able to find one that simply had the 3 RCA inputs and 1 coax output. It seems that these days that's not enough so the have added a second, unnecessary, coax input.
As I mentioned previously, I recommend the Radio Shack high isolation A/B switch:
A/B SwitchNot sure if it's still available at the stores but if you can find another high isolation A/B switch it should work just as well.