I'm sorry to inform you, but your post has to be one of the most vague ones in the whole internet.
Can you please inform us what you need help with? And then provide some relative info (the code with problem would be nice).
Thats a really big topic unfortunately. Seeing you already know how to code desktop software it won't be too big a leap however. Do you know HTML and CSS?
Create a web project in visual studio and for each web page you'll see two files, the .aspx (which is the visual aspects of the webpage where you code your HTML) and a .aspx.vb file (which is sometimes called code behind). The aspx.vb contains all of your server code.
I would suggest having a play. Open a project, go to the designer view of the .aspx page and drag controls onto the page. Double click them to create method stubs in the code behind. This will show you how to relate controls on the webpage to the code that does the actual functionality.
Online tutorials will help a lot too.