Hi.
You can read these two good articles:
1. ASP.Net 2.0 - Master Pages: Tips, Tricks, and Traps : it will help understand how master pages work.
2. Master Pages In ASP.NET 2.0. It will tell you how to use the Master pages in ASP.NET to building a professional web application with a consistent, easy to maintain layout.
Hope it helps.
Please remember to mark the replies as answers if they help and unmark them if they provide no help.
Yours sincerely,
Amanda Wang
Microsoft Online Community Support