This keyword in Java, how to use? [duplicate]

This question already has an answer here:

• How does the “this” keyword work? 19 answers

I know there is many "similar" questions like this, but I'm going to be more specific, I am seeing a lot code like that.

public void number(int number) {
     this.number = number; 

Question is, how this kind of code can help in development? I am not completely newbie, I know what "this" does, but I don't understand this code (and I see it everywhere).