Privacy Levels
Google Calendar displays a series of calendars, all of them color-coded and stacked together. This allows you to view or hide calendars as needed. It also allows you to set different default permissions for each calendar. That means you can decide whether a calendar is totally public (e.g., sales and promotions at a local business or events for a club or conference); shared with a few individuals (e.g., a family calendar or workplace collaboration); displays only busy or available information (e.g., client meeting requests); or is visible only to you.
All of those options actually stem from two choices: public or private. Within public entries, you have completely public calendars where all events are visible to everyone, indicating when you are busy or available. Within private calendars, you may choose to share select events or availability with other individuals. You may override these settings when you enter new events.
NOTE: You can create a calendar with one default behavior and change the permissions on an individual item. However, I’d caution you against that (other than inviting attendees to an event) because it’s easy to forget you’ve overridden a private calendar to have a public event. The safer bet is to stick with the default permissions of the calendar type you choose.