Need Help for Script in python between a mosquitto broker and sqlite3

I need to create a Python script for subscribe to a Broker Mosquitto topic and insert these DATA into a sqlite3 database... I'm a student in second year of I.T school and MQTT is a new technology for me... I've found some answers on the net but not specific enough... This script is interesting: http://ift.tt/1AXtL6x

So I tried to "replace" MySQL by sqlite3 but I don't understand the whole script. Can you, please, try to explain me?

P.S: I'm a French student, sorry for my English.