If you want to view the google maps, add the env variable REACT_APP_GOOGLE_API_KEY with a valid Maps JavaScript API (frontend)
If you want to get the coordinates when creating a place (by filling the "Address" input in the form) with the places route (POST), add an env variable GOOGLE_API_KEY with a valid Geocoding API key. (backend)
For the database, add valid MONGODB_USER and MONGODB_PASSWORD env variables (backend)