How to understand the "Anchor"?

The “left” means from the element’s pivotx to the parent’s pivotx? and the “right” means?

And in the editor , what is the white rec means?

The anchor represents where the element is positioned relative to the Screen.

As its 0.5, 1, 0.5, 1, it means the the left and right anchor positions is 50% from the left edge of the screen and the top and bottom anchor positions is 100% of the bottom edge of the screen.

With X position being 8 and Y position 130, it means that the element’s pivot is 8 units to the right of the anchor position and 130 units up of the anchor position.