i wanna create folder in one of my hard disc partition but i can't because I'm not the owner. How do I do this?
I will assume that you created a few partitions with Gparted, and you are not able to access them since the owner is root.
I had this problem myself and accidentally found a painless workaround.
Unmount partition, open Disks from dash, click the desired partition, then click the little gears > more actions > edit filesystem... and give it a new name. Mount back, and you are the owner for some reason.
The short answer is, you don't. There's no need for you to be manually creating directories in system paths, or to change the permissions of any of the folders or files in those paths.
If there is some specific problem you are having, which results in you thinking this action is appropriate, then you are likely hitting a bug, or trying to do something wrong based on bad information. Please ask a question instead about the specific issue you're trying to resolve with this course of action you're attempting to take, to get better answers.