Hi Visvanathan,
RF modules have in-built circuit to modulate your data and transmit. In receiver side there will be a demodulator also. Normally we have ASK and FSK modules.
If there are more than one transmitter or receiver in operation at the same time, you should use encoder and decoder. Use HT12D, HT12E pair.
A single transmitter, multi-receiver configuration is possible, but single receiver and multiple transmitter is impossible unless you implement some kind of a multiplexing scheme like TDMA.