Complex sentence: By using resonant circuits, different transmitters could be "tuned" to transmit on different frequencies, and a receiver could receive a particular transmission by "tuning" its resonant circuit to the same frequency as the transmitter.
Split into simpler sentences: By using resonant circuits, different transmitters could be "tuned" to transmit on different frequencies. A receiver could receive a particular transmission by "tuning" its resonant circuit to the same frequency as the transmitter.