The following applications are each very useful. What makes them particularly powerful however is the way they can be synced through iCloud to other Apple devices you may have. If they are properly set up, whatever you enter or edit on one will be reflected on your MacBook/iPhone/iPad and even your Apple Watch (via the iPhone). If you make an appointment on your iPhone for example, it will also appear on your MacBook Calendar. Similarly, you might add an address to Contacts on your MacBook and it will become available on your phone, iPad, etc.
25. Very useful - Create lists, notes, or scrapbook - worth mastering
26. Sync (turn on in System Preferences)
This means every entry will be synced through the cloud to all your other devices. Eg, from phone to iPad, Macbook, desktop etc.
Contacts (Address Book)
28. Adding contacts
29. Groups, email
30. Sync (turn on in System Preferences)
31. Add events
33. Calendars and subscriptions
34. Links to