introduce a source to learn linq to sql

thanks for your guidance

Lawrence Pond : can you explain for me how linqpad works???
thanks

Best way to learn Linq is to download a copy a www.linqpad.net

Abolfazl,
You can have a look at this also:

http://msdn.microsoft.com/en-us/library/bb425822.aspx

There are many online articles on LINQ to SQL but I particularly like this one as it explains both the underlying concepts and the practical implementation very well:

http://www.codeproject.com/Articles/215712/LINQ-to-SQL-Basic-Concepts-and-Features

If you don't know LINQ to Objects already, it may help you to learn this first and the above article contains a link to another article by the same author on this topic as well as a link to a further article on the more advanced aspects of LINQ to SQL.