Connecting a new model from PX4 to Qground

I’m facing an issue while trying to connect a new model I have created using the manual from here.
According to that, I need to Define an airframe configuration file. But in order to do that, I need to connect to PX4 some model - so Qground would be able to connect to it (and than creating a configuration file)…
What is the start point? How can I create a config file, without connecting the new model in the beginning?