Watch this video to see how the radio hardware works on the micro:bit:
send String
Sends a string to other micro:bits in the area connected by radio. The maximum string length is 19 characters.
radio.sendString("Hello!")
Parameters
- msg: a string to send by radio.
 
Example: Two-way radio
If you load this program onto two or more micro:bits, you can send a
code word from one of them to the others by pressing button A.  The
other micro:bits will receive the code word and then show it.
input.onButtonPressed(Button.A, () => {
    radio.sendString("Codeword: TRIMARAN")
    basic.showString("SENT");
})
radio.onReceivedString(function (receivedString) {
    basic.showString(receivedString);
})
    
See also
radio