how to send notifications to selected lcoations

hello eveyone.

i am building an app, that connects users according to their location.
for example, a user can define a location and send a notifications to other users in the same location.

i have searched for solutions in the internet, and found something about geofencing and fire base messages, but still i have got no idea how to use to use it in real working code.

I'll be greatful if you can help me using those solutions or find another methods for sending messages and notifications to other devices in the selected lcoations.

thanks.