Do you remember your old classical radio system? This radio was being used to listen to several programs like music, news bulletin, etc. A typical radio works in a unidirectional way. It can receive a radio signal but can’t transmit.
Walkie-talkies are a kind of portable radio. But you can receive as well as transmits radio signals by using walkie-talkies within confined areas. So they can communicate bi-directional using radio frequencies.