Externat MQTT Broker, Integration in HA

I’m just having a problem understanding. I have been using OpenHab (Raspi) for years and would like to get involved with HA. I have Aquara sensors and Shelly actuators. All devices send to an independent MQTT gateway (Raspi) via a Sonoff Zigbee gateway with Tasmota. The combination of OpenHab and MQTT works very well.

I would like to connect the external MQTT gateway to my HA.
Under “Integration” I integrated MQTT. With MQTT Explorer I see my gateway.

Now my understanding problem. Should the MQTT integration automatically recognize all paths or do I have to enter each sensor manually in a YAML file? There are several paths (Zigbee2mqtt, shellies, tele, tasmoda, …) There is a lot of information on the Internet, but I couldn’t see the concept behind it anywhere.

I thought HA would automatically detect the paths and offer me the devices so I could use them.