How can i start in shaders in unity 3d to make some effects?
For fixed function shaders, unity manual is all you need.
If you want to create Surface Shaders, you should have some knowledge in CG, take a look at the book below.
If you want to go with the Vertex Fragment shaders I would highly recommend a free online book by Nvidia
http://http.developer.nvidia.com/CgTutorial/cg_tutorial_chapter01.html