Welcome to App Inventor.
What have you done so far?
To allow users to interact in real time you will probably store data in a CloudDB, FirebaseDB or a Google Spreadsheet stored on your Google Drive and use these databases in conjunction with the MIT Map control or by using a Static Map with Google's Map API..
You did not find Social Distancing ... a CloudDB / Location Marker Tutorial which is similar to 'post announcements with a pin location and receive responses.' or How to: A Family Chat app built with the MIT CloudDB component which is live communication but without a map and does part of what you say you want to do.
and also how to click on Markers and get information ( see National Parks tutorial) and How can I select markers created on the map?.
..and an introduction to using information from a GoogleSheet is provide in the discussion Retrieve location specific Phone Numbers (or other data) from an appropriate Google Spreadsheet.
Good luck.
Regards,
Steve