How to send data through MQTT

Hi, I'm new to this GEN 1 Shelly 3EM device. I'm Trying to send data through MQTT. I have already done this whole process in Shelly Plus 1PM using scripts and everything. The problem I'm having is that I have connected it to the broker but after that I have no idea how to send my data/topics to broker and access the topics on where I'm trying to send it. Can somebody help me in this query?