Texture Coordinate Details
Texture Coordinates define how a 2D image texture map is applied to the faces of a group. Each vertex of each triangle has its own set of texture coordinates. If two triangles share a vertex, each triangle may have different texture coordinates for the same vertex.
Creating Texture Coordinates
Texture coordinates are created implicitly when a triangle is created. The default coordinates are not very sensible or useful.
Other Texture Coordinate Details
To change the way the texture is mapped onto a group of faces you will need to use the Texture Coordinates Window. Typically when using the Texture Coordinate Window you will start by selecting the "Group" map scheme. This method of setting up starting texture coordinates can be somewhat limiting. Sometimes using a Texture Projection gives you a better starting point for texture coordinate assignment.
After using a group map scheme or texture projection to get the texture coordinates in roughly the place you want them, you can use the viewport in the Texture Coordinates Window to select triangle vertices and move the coordinates. The viewport in the texture coordinates window follows most of the same conventions as the model viewports.