The +Google button in the right hand corner of the calendar is the recommended way to get Calendar on your Android phone or tablet. You first add the calendar via Google calendars on the web and then the calendar will show up in the app on your phone. If you are tech savvy and want to choose which calendars to subscribe to, use the steps below.
Step 1: Copy the address of the calendar you would like to add.
Step 2: Add the calendar to your google account
Step 3: View the calendar in the calendar app.