add_marker.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <style>
       #map {
        position: absolute;
        height: 100%;
        width: 100%;
       }
    </style>
  </head>
  <body>
    <a href="https://onethinglab.com/the-definitive-guide-to-google-maps-markers#marker-add">How to add marker</a>
    <div id="map"></div>
    <script>

      function add_marker(gmap, coordinates, text) {
        var marker = new google.maps.Marker({
          position: coordinates,
          map: gmap,
          label: { text: text }
          });

        return marker;
      }

      function init_map() {
        var places = {
          'UA': {lat: 50.43333333, lng: 30.516667},
          'DE': {lat: 52.51666667, lng: 13.4},
          'GL': {lat: 64.18333333, lng: -51.75},
          'JP': {lat: 35.68333333, lng: 139.75},
          'MG': {lat: -18.91666667, lng: 47.516667}
        };

        var gmap = new google.maps.Map(document.getElementById('map'),
          {
            zoom: 2,
            center: { lat: -25.363, lng: 131.044 }
          });

        for (var country in places) {
          add_marker(gmap, places[country], country);
        }
      }

    </script>
    <script src="https://maps.googleapis.com/maps/api/js?callback=init_map"></script>
  </body>
</html>