Here’s some useful information from this month’s meeting on Contacts and Calendars.
The contacts and calendars apps exist on both the Mac (computers) and iOS (iPad & iPhone). The different versions can cooperate and share data via iCloud, but they are not the same. The Mac version can do some things, such as edit contact groups that the iOS version cannot do.
Here is Apple’s Support Article on Contacts for the Mac. It is an overview of Contacts and how to use them.
And, similarly, here is Apple’s Support Article on Calendars on the Mac.
Besides Apple’s pre-defined Holiday calendar and your own calendars, you may find public calendars for various topics and groups on-line which you can subscribe to. For example, here is the MacMAD meeting calendar. If you subscribe to that, you will see our monthly meetings. If any changes are made, you will see the changes automatically.