When the source field is defined, Meteor will extract data from a metadata source using the details defined in the field. name field should define the name of Extractor you want, you can use one from this list here. config of an extractor can be different for different Extractor and needs you to provide details to set up a connection between meteor and your source. To determine the required configurations you can visit README of each Extractor here.

source:
  name: kafka
  config:
    broker: broker:9092

To get more information about the list of extractors we have, and how to define name field refer here.