> I am beginner of ASP.NET. I am following the quickstart tutorial provided from www.asp.net. It provide samples, but it is not explain in step by step basis. I am not familiar with VS.NET IDE yet. Therefore I face problem here.

THe quickstarts don't take a VS.NET approach. You can use the entire .NET Framework (which includes ASP.NET) with out using VS.NET, just using text files. So, create the files they suggest in notepad, save them with the proper extension (ASPX usually) and try and run them like they suggest.

If you need any more help with that, just ask here.

>I add a submit button to my web form. I would like to execute something once use click submit click. I set the submit button as server web control. Then, I doublclick it, VS.NET jump to C# code. If I coding here, will it converted to asp.net code?

C# code IS ASP.NET code! When an ASP.NET Web Form runs, it is really compileing and executing C#/VB.NET code.

>I back to .aspx file, and select HTML. Then, I select submit1, and onclick event from the dropdown combo above of the code. However, the submit1_onclick() is added with Javascript syntax. How to make it to C#? I need to change the function header by myself?

Well, in the HTML it will be Jscript, C# can't run on the client side. Only the Server side, so where you were before is where youw ant the code to work. For an introduction to whats actually happening with these Web Forms, take a look at http://www.levelextreme.com/Magazine/March2002/Page9.asp