The RF (radio frequency) input on an LCD television is typically used to connect cable TV service to the set. A coaxial cable attaches between the LCD set and a cable TV box with threaded couplers on the cable ends to hold the connection. Since LCD TVs usually have three or more inputs, use the remote control to activate the input for the RF connection.
Fasten one end of the coaxial cable to the "RF IN" jack on the rear connection panel of the LCD. Turning the ring on the cable end holds it to the external jack on the television.
Hook up the opposite end of the cable to the "RF OUT" jack on the back of the cable box.
Turn on the LCD set and the cable box.
Press the source button on the LCD TV remote control. The button may be labelled "Input," "TV/Video," "Source" or similar. Release and press the button until the cable box signal appears on the LCD.