Which side should I put the close button on a window? [duplicate]

1. Should close button be on left or right?
2. Which button is used to close the window in answer?

Should close button be on left or right?

The upper right corner of a modal window is the common place for the close button X in desktop experience.

Which button is used to close the window in answer?

(eXit button) Also called a "close" or "exit" button, clicking or tapping the X removes the current window, dialog box or popup message from the screen. It is also used to delete text and graphics.