You set the UV when you create the vertex.
A U or V co-ord goes from 0 to 1. Zero being the left hand side or top and 1 being the right hand side or bottom depending on if you're dealing with the U or V respectivly.
A U or V co-ord goes from 0 to 1. Zero being the left hand side or top and 1 being the right hand side or bottom depending on if you're dealing with the U or V respectivly.