Description:

MDI (Multiple Document Interface) form, in which we can view and work with several documents at once.
 
MDI_form.vb

Public Class MDI_form

    Private Sub MDI_form_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Me.BackColor = Color.Aqua
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim mdichild As New Data_entry
        mdichild.MdiParent = Me
        mdichild.Show()
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim mdichild As New customer_details
        mdichild.MdiParent = Me
        mdichild.Show()
    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        End
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Dim mdichild As New orderdetails
        mdichild.MdiParent = Me
        mdichild.Show()
    End Sub
End Class

Data_entry.vb

Imports System.Data.SqlClient
Public Class Data_entry
    Dim con As New SqlConnection
    Dim cmd As New SqlCommand
    Dim da As New SqlDataAdapter
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Me.Close()
    End Sub
    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        TextBox1.Clear()
        TextBox2.Clear()
        TextBox3.Clear()
        TextBox4.Clear()
        TextBox5.Clear()
        TextBox6.Clear()
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        con = New SqlConnection("Data Source=COMPUTER10;Initial Catalog=vb;Integrated Security=TRUE")
        con.Open()
        cmd = New SqlCommand("insert into dataentry values('" & TextBox1.Text & "','" & TextBox2.Text & "','" & TextBox3.Text & "','" & TextBox4.Text & "','" & TextBox5.Text & "','" & TextBox6.Text & "')", con)
        da = New SqlDataAdapter(cmd)
        cmd.ExecuteNonQuery()
        con.Close()
    End Sub
End Class