Dont understand some basic function!!

[quesxion]

glMatrixMode(GL_PROJECTION);
glLoadIdentity();

above statement is for what?? why need included GL_PROJECTION??

There are 2 different matrices, one for projection and the other for modelview. Some transformations are better suited to the first, others are for the second. You can do a search on this forum, I think this question has been answered several times.