Void in Java

It's quite simple: a method that returns void returns... nothing. Zilch, nada.
For example, the method System.out.println returns void, meaning nothing.
The result of the process will therefore be used in another way (in the case of println, displayed on the screen) but will not be something that can be returned in a variable. The method returns an empty set (void = empty in English) of elements.

Be careful not to confuse it with null (a mistake I made often in my early days, shame on me).
void is a sort of variable type that we only use for the return value in a method declaration:
example:

public void myMethod(int number){
System.out.println("I return nothing");//displays and returns nothing
}

whereas null is an object that represents something empty, a bit like the word "nothing" in French (like in "what gift did you bring me?" "nothing. just die.")
example:

public Object myMethod(int number){
return null;//returns the null object, meaning a null value, not even equal to zero
}

I hope I've shed some light on your mind.