Hi rlkubi,
The antenna and the cable TV share wiring. The two inputs come together at a signal booster, probably located near your entertainment center. There's a small red button that lights an LED when depressed. For antenna signals you need to have the signal booster ON. For cable TV it needs to be OFF.
On most TVs, the menu settings need to be switched between CABLE and ANTENNA, and you will typically also have to run a channel scan on the TV menu.