Every UI GameObject has a Rect Transform component as its first component. This component is very similar to the Transform component on non-UI GameObject, in that it allows you to place the object within the scene.
You'll note that when you first place a Canvas in the scene, you can't adjust the values within the Rect Transform, and there is a message stating Some values driven by Canvas, as shown in the preceding screenshot.
This message means you cannot control the position of the Canvas, because of the properties selected in the Canvas component. Adjustment of Rect Transform is disabled for Canvases that are in Screen Space-Overlay Render Mode and Screen Space-Camera Render Mode (determined by the Canvas component). ...
