Vehicle files to modify when sending a Mavlink message


I’ve been following this ( guide to send a new message through MavLink. I added a very basic message on the common.xml file where I’m just trying to send a basic int and have it display on Mission Planner, but I’m confused on how the interface between messages and Mavlink works. I understand that using gave me a mavlink_msg_ .h file, but what I want to do is use the protocol to send my message directly to Mission Planner (and preferably have it display on the screen). Basically, I’m lost on step 5 of the guide and don’t know where to start. Can someone provide some assistance?