To use google calendars you need to have a google account and add it to your Android phone.

To sync your Google Calendar data between Google cloud and the Android calendar storage, you need the Google Calendar app installed. (Early versions of Android included a Google Calendar sync adapter, but this was moved to the Google Calendar app, to be able to update via Google Play. Alternatively you can configure Google as CalDAV calendar, but this has several limitations.)

The Google Calendar sync to Android has some limitations:

Synchronization Bug in Google Calendar version 2022.02.0, 2022.04.1, 2022.06.1, 2022.08.0, and 2022.10.1

UPDATE: This bug is fixed with version 2022.10.2 (released March 21, may not yet be available for all users)!

The above listed versions of the Android Google Calendar app have a critival bug with regard to synchronization of recurring all-day events. Such events are synched to Android with a duration of 0 days (which is displayed as one day by aCalendar). This also leads to birthdays without contacts not correctly detected by aCalendar.

We have informed Google on January 23 and a fixed version has been published on March 21. If it is not yet available and  you don't want to wait, you can it from APKMirror.

Please see also: Problems with Google Calendar Synchronization