An introduction to MQTT

I've been using 1-wire temp sensing (to a balloonboard hub running plain Debian) since 2009. It works pretty well, although I've had to replace more sensors than seems reasonable over that time.
I acquired this temp/CO2/humidity sensor last year using the ESP 8266 base: http://vair-monitor.com/2017/01/06/vthings-co2-and-dust-m...

It all seems to work rather well, although I have failed to properly grok MQTT and connect thing together nicely. It's erm, 'on the list'.