Any link for a good and simple tutorial on shadows? I want to generate shadows for the following scene.
what!!! u wanna make parts of that even darker 
an easy/common method is shadowmapping
see http://www.paulsprojects.net/tutorials/smt/smt.html
If the geometry is static (doesn’t move), and the sun doesn’t move, then the easiest thing to do is to pre-calculate the shadows as a set of light maps, and render the scene with dual texturing (and no lighting). Use a light mapper like Giles, or a light mapping modeler like DeleD to generate the light maps.
I really like this tutorial. That Pauls Project’s tutorial is good too.
Thanks.