On your iPhone or iPad, go to Settings > [your name] > iCloud.
Tap See All (or Show All), then turn on Home.
You can now add HomeKit accessories in Home.
You can control your accessories from your iPhone and iPad if they’re on the same Wi-Fi network. If you want to control accessories remotely, set up a home hub. See the Apple Support article Set up accessories with Home on iPad and Set up your HomePod, HomePod mini, Apple TV, or iPad as a home hub.
For more information on how to control accessories and share access to your home on your Mac, see Home accessories website.