Programming in OpenGL

Hi
I know how to program in opengl, but still get stuck on how to go about in implementing algorithms. Please be assured that i know the basic concepts but dunno how to go about in implementation.
i hv to program in my assignment without using windows programming, in Opengl with C++ the following things::

1. Implement the Scan-line Z-buffer algorithm. Code should identify and
display the wire-frame of all visible surfaces of a given 3D object in any userspecified
projection type and transformations.
2. Implement the basic illumination model using a single point light source,
and use Constant shading. Input values include all the required constants such
as ambient intensity, light-source intensity and other coefficients, and choice of
light source vector and view vector. Keep in mind that the view vector should be
consistent with the view specified in the projection.
Display the shaded visible surfaces of a given 3D object in any user-specified
projection type and transformations.
3. Extend the system to include multiple light sources, Goraud and Phong Shading
options.

Any guidance will be helpful, im using visual studio 6 for programming in C++.
thanks
Pallavi