how to use md-calendar to highlight multiple date?

As I understand, You want to mark different event dates on calendar. As You can see in docs:

ng-model  will reflect the selected date object of the selected event date.  md-date-filter is very useful in your case to highlight event falling on the calendar date. You need to create a function with cDate parameter and return true or false. If it true date will clickable on the calendar otherwise disabled. Suppose you have array of event dates as:

var today = new Date();
  today.setHours(0, 0, 0, 0);
  var events = [
    today.getTime(),
    today.setDate(today.getDate() - 1),
    today.setDate(today.getDate() - 4),
    today.setDate(today.getDate() - 8),
    today.setDate(today.getDate() - 11)
  ];

You can create filter function in controller as

$scope.eventDates = function (cDate) {
    return events.indexOf(cDate.getTime()) > -1;
  };

Now,  in html use different attributes as :

<md-calendar ng-model="SelectedEventDate" md-date-filter="eventDates"></md-calendar>

And when you select or click on calendar date then SelectedEventDate will be populate to the related date. Do the something this as:

<div>{{SelectedEventDate}}</div>