Follow these steps to add calendars to your calendar.

  1. Open Google Calendar at calendar.google.com and sign in
  2. Click the plus sign "+" to the right of Other Calendars
  3. Click From URL 
  4. Copy and paste the calendar URL and click Add Calendar
  5. Click on the settings and rename them (School, Church, etc...)
  6. Return to your calendar view and use the checkboxes to show/hide these new calendars