Master pages in 2010

Question

I have a C#.asp.net 2010 webforms application that I need to modify. I have C# desktop experience, but I do not have C#.asp.net 2010. *Note I have read of asp.net books to update my skills. I have a master page that has root-> root-> root-> root-> root-> at the bottom of that page. I know that is the master page since the area is gray and i can not click on the 'root' items. I know the 'root' items are probably changed in the update_panel of ajax since there is a script manager also used. However, I to not know how the 'root' items are changed?

However I still have a few questions:

1. How can I find what code applies to each one of the 5 roots? I look at the source code (HTML), but I can not tell what applies. I know the 5 'roots' are like 5 tabs in a desktop applicatiom. What I see is what thec webpage is setup for. I believe this content place holder 4.

2. What I am looking for is probably content placeholder 2 or content placeholder3. Can you tell me how to tie the designer/code with each of the conent placeholders?

3. Is there a way I can step through this code to see how the controls are all wired together? At least step through code to the point right before the html is rendered by the browser?