Pairing devices
Pairing devices is sometimes tricky, since you need to reset the device to factory defaults and every manufacturer has different ways to achieve it. Please refer to the Zigbee2MQTT supported devices page for more information about pairing your device (https://www.zigbee2mqtt.io/information/supported_devices.html)
Once the plugin is correctly installed, two new switch devices will show up in your Home App: Permit Join and TouchLink. The two switches are off by default.
Before pairing a new device, you need to turn on the Permit Join switch. Once you tap the button, put your device in pairing mode (each device has different wait to go in pairing mode). When the ZigBee dongle finds a compatible device in its range, it will automatically mount it as a new HomeKit device. See the list of supported devices here. If the device is not supported, it will be paired but no HomeKit device will be created for you. Please read here on how to support new devices.
TouchLink is a feature of Zigbee which allows devices physically close to each other to communicate with each other without being in the same network.
Note that not all Zigbee devices support Touchlink, but most bulbs of common brands like Philips and IKEA support this.
This plugin supports Touchlink by creating a virtual HAP switch in the Home app. Once you turn on the switch it starts the Touchlink process, by scanning all channels to find compatible devices: this can take up to 1 minute and during this scan your network cannot be used. After some time the device will identify itself (e.g. a bulb will start blinking). This is especially handy for e.g. Philips Hue bulbs as they cannot be factory resetted by turning them on/off 5 times.