Java Constructor and Data Hiding, is all about the important part?

Your quote looks correct to me:

As I am a beginner, so far, I understood we have to use Constructor to initialize every new objects without writing manually and for Data Hiding (Encapsulation), we have to protect our class data variables and methods from unknown changes directly to that particular class.

About the question. I don't really understand what you are trying to ask ... May be you could re-phrase

Is this what those two functions is essential for every project, I mean I have to use constructor as well as getter setter for my projects

I'd say Constructor and getters/setters are essential to classes, not projects (don't really understand what do you mean by that) you create in Java.

Some classes can be used without constructors, if they have static methods like Integer.parseInt can be used without constructing new Integer class...

And you can sometimes if you need to create classes without getters/setters, in more advanced situations, when you get to 'Spring with Hibernate' course, or 'Intro to Spark' there will be examples...

Most of the time, Constructor+getters/setters is important to your "Model"/"Domain"/"Entity" classes, like Team, Project, Role, User... Classes that will have properties, and can be saved to databases...

So overall it is very important to look at every project independently ...

And there decide which class will look like. As I said, there can be classes without constructors, although I don't think that you will ever write those, although may be you could.

And can be classes without getters/setters.

I would say, If you decide, and go through treehouse 'Java' Track, or better 'Java Web development' Track you'll see a lot of examples of classes made by Craig and Chris, and will be able to see how classes should look like. Because only through concrete examples on concrete project will you be able to grasp the concept how and which class can be constructed