Question: I have just started web development.I want to make a screen to do basic add modify and delete operation.
The screen I've designed will have 3 tabs which will be add , display and delete.When I click on any of this tab a sub-screen should open for doing the operation accordingly. Another I thing I want to do is , I've a text field when I enter a number in it , I want to check for validation and tell him immediately if he's correct or not.
What controls I need to know to do this or how should I go about doing this?

Answer: 
Follow this tutorial on ASP.NET MVC to get started in ASP.NET web development.

<http://nerddinnerbook.s3.amazonaws.com/Intro.htm>

The tutorial will show you how to create a database for your application and how to interact with it in code. It shows how to create views (web pages) and actions for Add, Read, Update and Delete operations.
Hmmm... Controls to use. How about a [FormView](http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.formview.aspx) or [DetailsView](http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.detailsview.aspx), possibly a [DataGrid](http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.datagrid.aspx) and definitely some validators.. [RegularExpression](http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.regularexpressionvalidator.aspx) and [Required](http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.requiredfieldvalidator.aspx)...

And maybe watch some Asp.Net vidos... There are plenty here: <http://www.asp.net/web-forms> <--- This is where you should start.

Or you could use [MVC](http://www.asp.net/mvc) or [Dynamic Data](http://www.asp.net/dynamicdata)

Lots of choices...