People Nearby is an optional feature that allows Telegram users to explore local groups, find friends to chat with in their area, or quickly exchange contacts with people who are close.
You can find it in Contacts > Find People Nearby, as well as directly in the side menu on Android.
While you have the People Nearby section open on your screen, people who are very close will be able to see you there. If you don’t open the section, others will never see you in ‘People Nearby’.
You can also choose to permanently add your profile to the list of nearby people by tapping Make Myself Visible. After becoming visible, you can remove your profile from the list at any time by tapping Stop Showing Me.
Note: People Nearby is never turned on by default – users must manually enable it. If you are receiving messages from someone you don’t know, see Q: Who can contact me?