texture coordinates?

In one of the tutorials I found, it describes creating a cube that will end up being the background of a video game. The cube moves with the camera, so it never gets closer or further away. When setting the vertexes, it has commands for tu, and tv which "set the u and v components of the texture coordinate."

But WHAT IS A U AND V TEXTURE COORDINATE? I can't figure this out. I've been able to find out it has something to do with wrapping the background image, but nowhere I've found actually tells you what the coordinate is, what it does, why it's necessary in the program, nor what the difference is between them. Can someone PLEASE help me out with this? I'm completely stuck on this problem.

Here's a sample of some of the code they gave me if that helps (my problem spots are highlighted inblue) also, if you could explain thepinkhighlights a little too, I'd be most appreciative:

_topFaceVertex[0].X = -100.0f;

_topFaceVertex[0].Y = 100.0f;

_topFaceVertex[0].Z = -100.0f;

_topFaceVertex[0].Tu= 0.0f;

_topFaceVertex[0].Tv= 1.0f;

_topFaceVertex[0].Nx= 0.0f;

_topFaceVertex[0].Ny= -1.0f;

_topFaceVertex[0].Nz= 0.0f;

_topFaceVertex[1].X = 100.0f;

_topFaceVertex[1].Y = 100.0f;

_topFaceVertex[1].Z = -100.0f;

_topFaceVertex[1].Tu= 0.0f;

_topFaceVertex[1].Tv= 0.0f;

_topFaceVertex[1].Nx= 0.0f;

_topFaceVertex[1].Ny= -1.0f;

_topFaceVertex[1].Nz= 0.0f;

[2073 byte] By [Troy193] at [2007-12-26]