Need help with the Camera viewing

chang23

I am a beginner and i have recently started learning opengl .

so,please help me with the camera viewing and especially with gluPerspective ,i am having a lot of problems because of that.....

I had written a program that creates the image of the universe .i had created the orbits of the planets in the x-z plane and i wanna see it from upward i.e. from a point about h height from the x-z plane ..
this is my code -

#include
#include
#include
#include
#include

using namespace std;

void render(){
glClearColor(0.0,0.0,1.0,1.0);
// glEnable(GL_DEPTH_TEST);
}

GLfloat xrot = 360.0f,yrot = 0.0f,zrot = 0.0f;
void draw()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glTranslatef(0.0f,0.0f,-100.0f);
GLfloat x,z,angle,y = 0.0f;
glPushMatrix();
glRotatef(yrot,0.0,1.0,0.0);
glColor3f(1.0,1.0,0.0);
glutSolidSphere(7.0f,20,20);
glBegin(GL_POINTS);
for (angle = 0.0f;angle <= 3.1415f*2.0f*3.0f; angle += 0.08f){
glColor3f(1.0,0.0,0.0);
x = 30.0f*sin(angle);
z = 30.0f*cos(angle);
// y = 30.0f*cos(4 * angle);
// if (x < 5.0f && x > 5.0f )
glVertex3f(x,y,z);
x = 50.0f*sin(angle);
z = 50.0f*cos(angle);
glColor3f(0.0,0.0,0.0);
glVertex3f(x,y,z);

}
glEnd();
glTranslatef(-30.0f,00.0f,0.0f);
glColor3f(0.0,0.0,0.0);
glutSolidSphere(3.0f,20,20);
// glLoadIdentity();

glPopMatrix();
glRotatef((yrot),0.0,-1.0,0.0);
glTranslatef(-50.0f,00.0f,0.0f);
glColor3f(1.0,1.0,1.0);
glutSolidSphere(3.0f,20,20);

glLoadIdentity();
glutSwapBuffers();

}
void update(int x){
yrot += 0.75f;
glutPostRedisplay();
glutTimerFunc(33,update,0);
}
void reshape(int w,int h){
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
// glTranslatef(0.0,10.0,-100.0);
// glRotatef(90,1,0,0);

// gluLookAt(0,0,0,0,0,-100, 1,0,0);
gluPerspective(90.0,w/h,1.0,200.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
int main(int argc,char **argv){
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
glutInitWindowSize(800,600);
glutCreateWindow("chang");
render();
glutDisplayFunc(draw);
glutTimerFunc(1,update,0);
glutReshapeFunc(reshape);
glutMainLoop();
}

someone plese help me this ..
and also if u can explain me some about gluPerspective then it would be a lot more helpful...