Question of understanding configuration.yaml

If I want to install an add-on, e.g. Template Switch, how does this work with the new HA version? Example, Template Switch, it is recommended to insert the script into the configuration.yaml. But my configuration.yaml looks very “small” (see Printscreen). Where do the new “additions” have to be stored? under config /www/community/new? If the “additions” are stored separately, in a separate directory, it is certainly clearer and easier to correct errors.
What about the configuragtion.yaml?

Ok, for a start the Template Switch is an integration, not an add-on. They are very different things when talking about Home Assistant.

You can put the template switch configuration directly under scene: !include scenes.yaml in your configuration.yaml file.

Or if you want to keep your configuration.yaml file organised a bit better put this under scene: !include scenes.yaml

switch: !include switches.yaml

Then create a new file in your homeassistant directory called switches.yaml.

You can put the template switch config inside that file. Make sure not to include the first line (switch:) if you do it that way though.