i really dnt knw what is the difference between data table and data set and y we use them

a dataset can contain many datatables and relations between them. Additionally you can have a strongly typed dataset where it knows what columns are in the table, and you get automatic type checking at design time.

Vb.net 2005, Teradata, Sql Server 2005, mainframe automation

As MaslowB said, a datatable represents a single table from a database. Where as a dataset can represent many tables. The same methods and functionality are in both DataTable & DataSet.