With GMaps.js you can add markers this way:

  lat: -12.043333,
  lng: -77.028333,
  title: 'Lima',
  click: function(e) {
    alert('You clicked in this marker');

latitude and longitude are required. You can also attach additional information with details, which will be passed to Event object (e) in the events previously defined.

NoteIf you want to show an Info Window, you must add:

infoWindow: {
  content: '<p>HTML Content</p>'