A nice article written by DotNetGuts discuss these points about Web Services in .NET

• What is Web Service?
• History of Web Service or How Web Service comes into existence?
• Example of Web Service
• Web Service Communication
• Advantages of Web Service Communication
• Terms which are frequently used with web services
• Example of Creating Web Service in .Net
• Example of Testing Web Service in .Net
• Few Facts about Web Service in .Net

Read it @ DotNetGuts