first you should buy some basic asp.net books to understand the core concepts of asp.net application. Then crate some basic simple application and play with basic controls like
textbox,button,radio button,dropdownlist,gridview etc. Then you should start professional programming.
It is very easy for you just need to see the asp.net application and pages lifecyle. You are fimiliar with programming in c# and vb.net as you are doing winforms programming.
ASP.NET Webforms are also event driven. So its will work for you.
