For this tutorial you need an Arduino Ethernet or an Arduino UNO with an Ethernet shield. To complete this tutorial you need the following components.

Hardware Setup

This schema represents the led, resistor and pushbutton setup. With this setup each time you press the button, the LED is turned on and off.

Lelylan Setup

Open Lelylan Dashboard and create a new device by following 3 simple steps (if you are new to Lelylan, you can sign up for free).

1) Set a meaningful name (e.g. bedroom light).

2) Choose the device type. For this tutorial choose Basic Light.

3) Choose “Connect with MQTT” as connectivity option.

4) Get the Device ID and Device Secret.

Source : http://lelylan.github.io/lab-projects/arduino-ethernet-light/#code