Check this one out (won't necessarily answer your questions, but will come in handy later on):
http://www.heppler.com/shader/shader/index.html)
And what comes to your other questions, I suggest you remind yourself of the fact that your game came shipped with a plethora of shaders. You can access them all with the trusty old Notepad (that's the best shader editor) or ShaderEd to see them in action. Study them, copy them, alter them, and you will get a good grasp of shaders. After that, you can come and ask spesific questions to get spesific answers.