Xiaomi Home is the app used to set up and manage Xiaomi devices, such as a Wi-Fi repeater.
During the setup process, it helps connect the repeater to your modem/router: you select your home Wi-Fi network and enter its password. The repeater saves this information and then connects to the network to extend its range.
Once setup is complete, you can often uninstall the app; the repeater retains its settings and continues to function on its own. The app is primarily used for the initial installation, checking the repeater’s status, or adjusting its settings. If you do remove it, you can always reinstall it later if needed.