The calendar, with its useful reminders, can even be used to remind you of small tasks you need to achieve during a day.
This is important to train our users to properly use their Google calendar to enter their vacation (or meetings). This should be done at least in their own calendar so that their colleagues can know their availability. But ideally, a group calendar can be used to easily see who, in a team, is going to be busy or available at a given date.
The main calendar offers settings. These settings include the calendar language, time zone, and default meeting duration. Note that any additional calendars you add have their own settings. Be sure to check the notification settings in those calendars to stay informed about changes to events in a shared calendar.
When you create an event and add another person, Google Calendar will automatically add a Meet room. This can be confusing if the meeting is taking place on Zoom. So be sure to remove the Meet link and add a link to the Zoom room.
A useful feature in Google Calendar is the Find Time 
It's a good idea to encourage users to respond to invitations—whether by accepting, declining, or selecting "Maybe." This will help the host know who will be attending. They can also suggest a new time if the original time doesn't work.
Group calendars and resources. Group calendars allow you to book important dates for a special purpose for a group of people. This calendar can then be added on Google Calendar for those who need to have this information. For example you might want to create a Group calendar for the vacations in your entity and or a group calendar for important meetings.
Resources are something different. You can ask GTIS to create a resource for a car, a physical room, a virtual room such as a Zoom room, a video projector etc… Then, when you create a calendar event, you can book this resource at the same time.
To book a resource, when creating a meeting click
or click the Rooms tab if you see more options.
Working hours and location. In Google calendar you can set your working hours. Doing this will allow your colleagues to see if the meeting they invite you to join is inside your working hours or not. This is especially important when working across multiple time zones. You can find this setting in Calendar settings
Do not forget to set your own Time zone correctly. You can even add someone else's Time zone to quickly show what time it is in your colleague’s country.
It can be interesting to add other calendars.
You can browse resources calendar
You can add calendars of Interest
Or add a group calendar
Ask someone to send you the public URL of the calendar, open it, and at the bottom right corner click 
It might be helpful that some specific people share their calendar with someone else, like the Director with his/her assistant. You can either share their calendar or show them how to request access to someone else's calendar.
Note that the "Tasks" calendar appears last in the list of calendars. This calendar lets you specify the tasks you want to complete. In the left sidebar, there is also a "Task" icon that lets you view your tasks. When creating an event, you can specify that it’s a task-type event. You can’t add guests to this type of event—it’s just for yourself. This feature can help you stay organized and make sure you don’t forget important things...
Notice that if you press the ? key you will open the shortcuts keys help, which contains helpful information on how to jump quickly and easily to a calendar feature.
Finally, you can add your Google account to your smartphone. If you turn on notifications, you'll receive reminders on your phone for meetings that are about to start. This can help ensure you don't miss any meetings by alerting you when you're away from your computer.
Resources:
You can look at this video for more tips on Google calendars.