Hello,
Ok so this is a power feature first and foremost..
Second, by default they use what is built by us by default or a template override if you have had a developer of purchased an events template.
For additional fields, you would install the JEvents Custom Fields plugin and build them as you wish.
Then they will be auto included, you can tab them and not need to edit the Event Edit Custom Layout. However, if you need to change the positions and refine where they show you need to use the Event Edit Custom Layout and included the fields from the dropdown.
Many thanks
Tony