First, Google Calendar has two types of calendars: main and secondary calendars.

There are several differences between these:

*1 Event sync between Garoon Scheduler and Google Calendar

Your events are synchronized between Garoon Scheduler and Google Calendar. Thus, an event added to one of the two will also be created in another.

When events are synced from one to another, their visibility options are translated into the corresponding settings, as shown in the table below (click to enlarge):

Note:
・The default visibility setting for Google Calendar events is "Default visibility," which corresponds to "Public" in Garoon Scheduler regardless of your sharing settings for your main Google Calendar.
・If you'd like to keep your event private in Garoon, you must make it "Private" when you create one in Google Calendar.
・If you choose to make your event "Public" in Google Calendar, it means anyone on the Internet, whether on- or off-campus, can see it.
・You cannot sync a secondary calendar with Garoon Scheduler. Only your main calendar is covered.
・Google To-Do list and Tasks are not synced.

*2 Events from Gmail

Events from Gmail is turn on by default.

This feature finds flights, concerts, restaurant reservations, and other events in your Gmail messages and automatically add them to your main calendar. (Events from Gmail are added as a private event both in Google Calendar and Garoon Scheduler.

If you don't want Google to add events for you, you can delete events individually or disable this function.

For more information, see Events from Gmail (Google Calendar Help).