View the vidoes on "Working with Stylesheets and Master Pages" to understand the way content is layed out. .
http://www.asp.net/learn/videos/video-09.aspx
http://www.asp.net/learn/master-pages/
Then check out the video on "Working with the GridView and FormView" as most pages are using the GridView.
http://www.asp.net/learn/videos/video-07.aspx
That is just a starting point and I would also look more in depth about using themes.
http://www.asp.net/learn/videos/video-44.aspx
Viewing these videos will save you tons of future questions. After that it starts getting more involved.