Automation Actions

When an automation rule fires, it calls a service. For this service you can specify the entity_id that it should apply to and optional service parameters (to specify for example the brightness).

automation:
  # Change the light in the kitchen and living room to 150 brightness and color red.
  action:
    service: homeassistant.turn_on
    entity_id:
      - light.kitchen
      - light.living_room
    data:
      brightness: 150
      rgb_color: [255, 0, 0]

automation:
  # Notify me on my mobile phone of an event
  action:
    service: notify.notify
    data:
      message: Something just happened, better take a look!

If you want to specify multiple services to be called, or to include a delay, have a look at the script component. If you want to describe the desired state of certain entities, check out the scene component.