vb.net Imports namespace, help please ?

imports System.Data

imports System.Data.OleDb

imports System.Data.SqlClient

For the .net system namespaces, is there a quick reference of them all, and when to use them ?

I see them attached to codebehind examples yet I cant figure out what system namespaces mean, or when to use them ?

I am vb.net newbie from vb6.0??
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