Create YAML script under “CREATE NEW SCRIPT”. How exactly?

I would like to create a script under “CREATE NEW SCRIPT” under Scripts that sends a GET command:

How does it work? What exactly does the complete YAML script have to look like?
Do I have to enter something in the file: /homeassistant/configuration.yaml? If yes, what?

The first step is going to be setting up a service that sends your command.