Position is the in-world position.
Texture coords is the coords that map to that position.
Erm.. that sounds..
So if you have a quad with positions as follows: 0 0 , 0 10, 10 10, 10 0
and texture positions as: 0 0, 0 100, 100 100, 100 0
then the 100x100 rectangle of texture would map to a 10x10 rectangle on screen.