This easy to understand code snipped shows you how to add a MDI Child Form to your MDI Container (or parent) Form.
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
' Dinamically create a new Form called Form2
Dim Form2 As New Form
' Tell Form2 to have aparent (Form1), means it has to be displayed inside Form1
Form2.MdiParent = Me
' Add Caption to Form2
Form2.Text = "Form2"
' Show Form2 (inside the client area of Form1
Form2.Show()
End Sub
End Class