I am still not sure how does this compareTo function is getting called internally

"how does this compareTo function is getting called internally"

-> What I'm getting here is that you want to know, how come that we implement the compareTo function in a class, but yet we are calling the same compareTo function internally, to get the result? - well, we are doing this because in the class we have created, there are many fields on which the comparison could be calculated on. For example, if there would be a "TreehouseStudent" class, and you and me were objects, we could be compared by our name (alphabetically), our age, our Treehouse Points. So we have to specify what data would do the comparison, when comparing objects of our own custom made class. And the reason we can use the same method inside is that in classes, which are part of the Java language core (String, Date, int.... etc), compareTo already has been implemented.

"how does the return statements are contributing to the comparison we want to achieve here"

-> Basically, if you have an array with objects of a particular class, you can call a "sort()" method on that array. Now this "sort()" method has such a code that it can only sort if the Comparable is implemented in that class which it is about to sort. This "sort()" method will know very well how to use this compareTo method, it will compare two objects, if the result is -1, the first goes one step back in the queue... etc.

I hope this makes sense! Much love! Keep up the good work!