what different between absolute positioning and relatives positioning in css

Answer 1

Absolute uses coordinates of all page(or canvas) to determine position
And relative uses the position of supporting block
For example:
You have some square somewhere in the middle of screen
You want to place a smaller square in top-left position
Absolute will place this little square in the top-left corner of page
And relative will place it in top-left corner of the first square

Answer 2

What if there is no square in the middle of screen?