Okay I can guess why we have misconceptions here. What texture I have is a SINGLE png for which I have already put all my sprites in it. (like Wooden Atlas.png)
And I guess how you produce a new atlas is putting all SEPERATE png sprites inside the project and choose those png one by one inside Atlas Maker and auto-generate that all-in-one png.
Am I right?
EDIT: Guess I am right, I put all my pngs inside another folder and add them one by one in Atlas Maker and the large png is generated by Atlas Maker. Hope this help other people who have misconception here.