Need help to learn vB 4 Add-on / Plugin Dev

[Power_user_EX]

Hi ,
I am into PHP programming and want to learn vB Product/Plugin/Add-on Development ... have a few basic questions :

1) I want to know that How do Templates , PHP Plugin Code , Variables work with each other.. I can make sense of them If i consider them in isolation but confused when i try to visualize them as working with each other.

2) Is there a list of predefined vB variables like $vBulletin[] that i can refer ?

3) Any tutorial for making Variables(options) in AdminCP->Settings and using them in the plugin code ?

-Regards