GLvoid gluPerspective( GLdouble fovy, GLdouble
                       aspect, GLdouble nearClip, 
                       GLdouble farClip )

Notes:

gluPerspective creates a viewing frustum using glFrustum. You just provide the information in a different way. glFrustum provides more flexibility in that it allows you to specify a frustum that is not symmetric in x and y. This means that the line of sight does not have to be centered in the middle of the projection plane.

near and far are the same, but instead of specifying left, right, bottom, top, you give an angle for the field of view in y (fovy) and the aspect ratio. fovy determines the height, and the height combined with the aspect ratio determines the width

• Large fovy is like having a "wide angle" lens
  
  
• Small fovy is like having a "telephoto" lens
  
  

aspect determines the width of the frustum.