Focus is a way to restrict notifications, calls and other interruptions for certain activities or situations. Like sleep, or driving or when you simply don't want to be disturbed.
The Person icon normally means you have a custom or personal Focus active or it was the last focus type that was active. If the circle in control center is white, the focus is active. If its gray its not active.
You can change which focus is active by tapping on the word "focus", and selecting a different focus from the list.
If you tap on the icon, it turns that specific focus on, without needing to go into the list.
You can edit and add Focus types in Settings ➜ Focus.
See the support document you posted from for more details.