It's good that you found a book you can use to help you learn Java.
But the Java API docs are the best place to get info about classes and methods that belong to Java.
A simple web search for 'calendar.getInstance' returns the following link as the FIRST RESULT
Then search that page for 'getInstance' and you will find this
Gets a calendar using the default time zone and specified locale.
and that link takes you further down the page to this
public static Calendar getInstance()
Gets a calendar using the default time zone and locale. The
Calendarreturned is based on the current time in the default time zone with the default locale.
- a Calendar.
That shows that 'getInstance' is a static method that returns an instance of the 'Calendar' class.
Examine the API and you will see there are more methods named 'getInstance' that each take different parameters.
Those methods are FACTORY methods. You use them as a 'factory' to create objects. The 'factory' you use determines the exact characteristics of the object that gets created.
Just as a car 'factory' can create blue cars a different car factory might create red cars, or one might create an electric car and another a diesel.
Different factories for different objects. The objects have a LOT in common but can have different characteristics.
The NEW operator just creates a VANILLA object using all of the default characteristics.