Not sure I understand the question correctly.
Very simple examples of how to assign uv coordinates:
http://threejs.hofk.de/BufferGeometry/02_buffer.html
http://threejs.hofk.de/BufferGeometry/01_buffer.html
(see also Collection of examples from discourse.threejs.org)