What actions of plugin WordPress ?

hi everybody,

At present, I am using Twenty Ten WordPress, now I am learning to write and design WordPress Plugins, but I don’t know about actions of Plugin WordPress clearly, Ex: What is index.php file displaying ?, What is Page.php file displaying ? .v.v…
At present, want to know that what is file to display contents of admin page, what is file to display contents of main home page ?
Can you tell me about that or give me some documents ?

Thanks you very much!