How to create a button to send an MQTT message

Configuration Frontend
1

I am referencing this page:

I have added the following to the mqtt block in configuration.yaml:

mqtt:
[...]
  button:
      name: "Open Gate"
      unique_id: gate_switch_btn
      command_topic: "test/relay1/cmd"
      payload_press: "relay1=on"
      qos: 0
      retain: false
      entity_category: "config"
      device_class: "restart"

and rebooted Home Assistant, which does not complain about any error.
The page linked above says “when the button is pressed in the frontend or the button press action is called” but I do not see a button?
Where is the button?
How do I “call the button press action”?
Note: I have a number of sensors reporting via the HA MQTT broker and that part works fine. I can send manually a message to the relay board (from another computer with an MQTT client) and it does get the message so I know that part works too.
Note 2: I am a complete noob with HA so thanks in advance for your patience…
TIA for any help…

2

Put the entity open_gate in an entity card or entities card or even a button card. Similar to how you’d put a script or switch in a card.

5

This is what I did after creating the button entry under mqtt:

  1. In configuration.yaml, add the button definition as described above. Save the file.
  2. Open the dashboard where you want to place the button and click the Edit icon at the top right.
  3. Create a new section or use an existing one, click the button with a + sign.
  4. This will open a drop down list of available card templates. Select the kind of card you want, I selected Button.
  5. Once the Button card is open, click the drop down box called “Entity” and select the button you just created.
  6. In the Tap Behavior box, select “Perform action” and under “Action”, select “Button: press”
  7. Under Target, click “Choose entity”. This will open a drop down list of available entities. If it does not, you may need to reboot HA and verify there are no error messages. Select the button you created at the first step.
  8. Under “Hold Behavior”, select “Default”.
  9. Save the Button Card
  10. Click the “Done” button at the top right of the dashboard.
  11. The button should be visible on the dashboard.