MQTT is a great IoT protocol that uses topics. A lot of the DIY smarthome environments have gone down this path verses direct proprietary protocols such as Zwave, Zigbee and even Wifi (perse').
I used this for my Salt Tank project using an arduino WeMo D1 and a Ultrasonic Sensor.
The biggest benefit to MQTT is speed. All devices listening on a topic receive the message at the same time. For lights this eliminates the popcorn affect the other protocols suffer from as all the lights receive the message to do something and they do it at the exact same time.
If you do some simple YouTube searches for "MQTT Smarthome projects" you will see a ton of great IoT solutions to 1st world problems that are significantly cheaper OR don't exist as a solution today.
To get started you will need an MQTT broker installed on a RPi. This is the "hub" of the MQTT messages. Once this is done install a MQTT Explorer to see what is going on in the MQTT hub. Probably not much without a client BUT with the tutorial I sent you above you can goof around and begin to understand the use cases.
Hope this helps!
