Since you've specifically asked about a client server web application, what you really need to google/bing for is how web servers work. Since this is a Microsoft technologies site, I'd assume you would want to search for ASP.NET.
Note that this is different from the traditional use of the word, where client-server design typically meant you had a server on the network, and client apps that would connect to this server. In very simple cases, the server would merely be the database server and clients directly talked to the DB. These days, this would be severely frowned upon as a very poor practice. In slightly more sophisticated designs, clients communicated to a server app (via sockets, remoting, wcf etc.) and the server app shielded the actual database from the end clients.
Oddly enough, the wikipedia page does not have too much direct content (
http://en.wikipedia.org/wiki/Client%E2%80%93server_model[
^]) but there are links from the article to related topics, so you may want to take a look at that as well.
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