Using 2d coordinates, a vertex is mapped to a position on the texture. Usually coined "u" for the x axis and "v" for the y axis on the texture. Well seems opengl uses s and t. The legacy way of setting it for a vertex anyways: http://www.opengl.org/sdk/docs/man2/xhtml/glTexCoord.xml .
I'm almost certain any number of tutorials that have been linked to you goes over this, have you tried reading them ?
Put it so the corners go to the corners of the texture ? It's a 3D model flatted onto a 2D surface, that's all there is to it. Like those exercises they make you do in kindergarden, there's a layout of the cube on a paper you cut it out and fold it and you get a box. Well that outline on the paper is what you are trying to create. You have to choose where the points of the cube go on the texture and the texture will be drawn on the cube in that way.