How does UV unwrap works?

how do I know which part of my 3D model should I mark a seam so I could unwrap it and textured it later? any advance tutorial on uv unwrapping? it really confuses me…:spin:

http://wiki.blender.org/index.php/Doc:Manual/Textures/UV

Some tutorials for blender 2.5 but the uv unwrapping principles are exactly the same in 2.49





thanks you guys! :slight_smile: