What is the basic purpose of Google calendar?

The basic purpose of a google calendar is basically the same as a regular calendar. it is used to keep track life's important events all in one place.

The basic purpose of Google Calendar is to provide people with an electronic calendar, in a format which is more commonly used today as opposed to paper technology. It acts just as a regular calendar, but also enables the ability to place reminders on specific dates, place event locations, and invite other users to events via nontifications.