From ComputerCraft Wiki
The rednet API provides a simple computer networking model over RedPower bundled cables.
|rednet.open( side )||Tells the computer that the side can be used for networking.|
|rednet.close( side )||Tells the computer that the side can no longer be used for networking.|
|rednet.announce()||<no description given>|
|rednet.send( receiverID, message )||Sends a message to the computer using the opened sides.|
|rednet.broadcast( message )||Sends the message to ALL computers.|
|rednet.receive( timeout )||Receives packets. Usage: senderID, message = rednet.receive(5) and the like. It sends the ID of the sender, and the message.|
You can also handle the "rednet_message" event to receive messages without calling receive(), the arguments are the same as the receive() return values.