Zigbee is an independent radio standard. Just like 433MHz, WiFi, Bluetooth, etc. In general, a bridge or hub is required, which is connected to a standard router.
Zigbee, however, is more energy efficient than Bluetooth and WLAN. It has a very good range. Vmany devices use this protocol. It is flexibly expandable and passes commands that are not intended for this device. So it spans a network (mesh network) across all known smart home devices.
With the Sonoff Zigbee Bridge, you can pair your Zigbee devices and sensors and conveniently integrate them into the smart home network.
The Tasmota version of the Zigbee Bridge easily integrates with most smart home applications via the MQTT protocol in a cloud-free manner. Including: ioBroker, openHAB, FHEM, NodeRed, Home Assistant, Domoticz, among others.