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  I'm not really understand what  do the1)MatrixMode and Projection Matrix2)MODELVIEW and modelview matrixglViewport(0,0,width,height);// Reset The Current ViewportglMatrixMode(GL_PROJECTION);// Select The Projection MatrixglLoadIdentity();// Reset The Projection Matrix// Calculate The Aspect Ratio Of The WindowgluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);glMatrixMode(GL_MODELVIEW);// Select The Modelview MatrixglLoadIdentity();thanks   
  The projection matrix basically determines what the point of view looks like (similar to your eyes), while the modelview matrix determines what everything looks like (like the world around you). Setting the matrix mode simply switches between these two, and the changes you make to them (translating, rotating, etc.) determine how everything looks when rendered. Hopefully that answers your question.   ;  You can liken the modelview and projection matrices as tripods since, like with matrices, a tripod you can move around and rotate whatever that's attached to it, effectively being able to freely position it somewhere inside a room. Of course unlike a tripod, with a matrix you can also scale and shear whatever it's "attached" to. It's not a perfect analogy [smile].So, imagine that the viewpoint, "camera", of your 3d-scene is attached to one tripod and whatever object you are drawing is attached to another. Then the projection matrix controls the position and rotation of the tripod attached to the camera while the modelview matrix controls the tripod attached to the 3d object you're drawing.glMatrixMode just sets which one of the matrices you are going to manipulate. Then using methods such as glRotate and glTranslate you move around the current tripod.Changing the modelview matrix for each object you draw, you can set it up so that the different objects in your scene sits on different tripods and can be positioned and rotated individually. Using glPushMatrix and glPopMatrix you can even attach tripods to each other in complex chains.Anyay, enough of the tripod analogy. I'd advice you to read up on the subject in the chapter on viewing (chapter 3?, at least in the older revisions) in the OpenGL red book as well as brush up on linear algebra and matrix math.   