I can set a texture in the UV/Image editor window, and it appears in the model view window applied to the model (when in textured mode), and I can also set textures as part of a material which is used when rendering with F12.
Can anyone explain why a texture can be set in two places? What is the purpose of each?
Setting a texture using the UV editor is a quick way to get a texture on the model that you can see in the 3D window while editing or animating. It also used to be the only way to get textured surfaces in the game engine. You can set ‘TexFace’ in the material settings if you want this texture to appear in the final renders, but most of the time it’s just an aid to visualisation while working on the model. For example, you might use a test grid this way to check that a UV mapping is not too distorted.
Using the texture channels in the material settings is more work, but gives you much more control over the final appearance, so is normally preferred for rendering. This way you can layer multiple textures, and change both the way they map to the surface and what properties of the surface they affect.