Relationship between Window size/ screen size / Logical size

My Android device supports the resolution of 480800 ie: (Widthheight).

i am trying to display 1280 * 720 frame that are received from ffmpeg.

Pertaining to SDL:

  1. Window size is created to : 640 * 480 ( width * height ) 2) Renderer size 640 * 480 ( width * height )

  2. Setting Logical Size to 640 * 480 [ SDL_RenderSetLogicalSize ]

Question:

  1. How 1280 * 720 [ HD Frame] actually related to these three components? What i understood is that SDL_RenderSetLogicalSize will try to fit (1280 * 720 ) into (640 * 480).

  2. Changing render size and window size does not create any difference. so what imporant it is about size of window/renderer and logical size ?

Thanks for you support.