imports system
imports system.data
imports system.data.sqlclient
imports dataset1.

And in Page_Load..
dim con as sqlconnection
dim cmd as sqlcommand
dim adp as sqladapter
dim data as dataset1
con.connectionstring="Provider=SQLOLEDB;initialcatalog=preethi;database=ACER;integrated security=true"
cmd.connection=con
cmd=new sqlcommand("select * from emp"),con
adp=new sqldataadapter(cmd)
adp.Fill(data)

'since i have only 3 fields
textbox1.text=data.tables(1).rows(0).item(0)
textbox2.text=data.tables(1).rows(0).item(1)
textbox3.text=data.tables(1).rows(0).item(2)

In Insert button-click event.....
' its bcoz the second textbox has numeric value and 1st and 3rd have only string values.

cmd = new sqlcommand("insert into emp values( ' " & textbox1.text & " ', " & textbox2.text & ", ' " & textbox3.text & " ')" , con
cmd.executeNonQuery()
Response.write(" One record inserted").

Imports System
Imports System.data
Imports System.data.sqlclient
'XXX used a standard  dataset since I do not have yours Imports dataset1 
Public Class WebForm1
    Inherits System.Web.UI.Page

'XXX con needs to be in scope when the Insert-Button Click event is handled    
Dim con As SqlConnection 

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'XXX Dim con As SqlConnection 
        Dim cmd As SqlCommand
        Dim adp As SqlDataAdapter 'XXX use SQLDataAdapter Dim adp As sqladapter
        Dim data As DataSet

        'XXX I do not have your database, please change connect string as required. 
        'XXX If you use the SQLClient dataprovider, you do not need the provider keyword.
        'XXX instantiated the con object
        'con.ConnectionString = "Provider=SQLOLEDB;initialcatalog=preethi;database=ACER;integrated security=true"
        con = New SqlConnection
        con.ConnectionString = "database=.;initial catalog=contacts;user=ASPNET;"

        cmd = New SqlCommand  'XXX instantiated the command object 
        'XXX connection is assigned below
        'cmd.Connection = con  
        'XXX cmd=new sqlcommand("select * from emp"),con
        cmd = New SqlCommand("select * from contacts", con) 'XXX

        adp = New SqlDataAdapter(cmd)
        data = New DataSet 'instatiated dataset
        adp.Fill(data)
        
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnInsert.Click

        Dim sSQL As String = "INSERT INTO contacts( contactid, firstname, lastname) VALUES (20, 'User20', 'User20Firstname')"

        Dim cmd As SqlCommand = New SqlCommand(sSQL, con)
        con.Open() 'XXX connection must be opened before command is executed
        cmd.ExecuteNonQuery()
        con.Close() 'XXX 
        Response.Write(" One record inserted")

    End Sub
End Class

Private Sub btnInsertDirect_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
    Handles btnInsertDirect.Click
        Dim iRet As Integer
        Dim iNextId As Integer
        Dim sConnectionString As String = "server=(local);database=contacts;user=ASPNET"
        Dim conn As New SqlConnection(sConnectionString)
        Dim sSQL As String

        sSQL = "INSERT INTO contacts (contactid, firstname, lastname)" & _
           " VALUES (@contactid, @firstname, @lastname)"

        Dim cmd As New SqlCommand(sSQL, conn)
        iNextId = 123
        cmd.Parameters.Add(New SqlParameter("@contactid", 123))
        cmd.Parameters.Add(New SqlParameter("@firstname", txtFirstName.Text))
        cmd.Parameters.Add(New SqlParameter("@lastname", txtLastName.Text))

        conn.Open()
        Try
            iRet = cmd.ExecuteNonQuery()
            litMsg.Text = String.Format("Inserted {0} records", iRet)
        Catch ex As System.Exception
            litMsg.Text = String.Format("Error: {0}", ex.ToString)
        Finally
            conn.Close()
        End Try

    End Sub

Private Sub btnDeleteDirect_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDeleteDirect.Click
        Dim iRet As Integer
        Dim sConnectionString As String = "server=(local);database=contacts;user=ASPNET"
        Dim conn As New SqlConnection(sConnectionString)
        Dim sSQL As String

        sSQL = "DELETE FROM contacts WHERE lastname = '" & txtLastName.Text & "'"

        Dim cmd As New SqlCommand(sSQL, conn)
        conn.Open()
        Try
            iRet = cmd.ExecuteNonQuery()
            litMsg.Text = String.Format("Deleted {0} records", iRet)
        Catch ex As System.Exception
            litMsg.Text = String.Format("Error: {0}", ex.ToString)
        Finally
            conn.Close()
        End Try
    End Sub