How to make multiple arduino boards to send and receive data with a computer ?

I'm new to Arduino. I have 4 Arduino boards separated connected to local network with a computer using Ethernet Shields. I want to be able to send and receive serial data, for example if one sensor connected to Arduino board number 1 (for example) was triggered it will send to computer instantly something like "Sensor1Triggered" . At the same time i can send data to any one of the 4 Boards to do any action like opening a relay for example.
I would be grateful if you guided me what is the best way to do that through Ethernet shield and how to configure it ? Thank you in advance