If the Sub is in the Code Module of the Userform you can refer to the form as object "Me" this will resolve to the parent form.
Private Sub CommandButton4_Click()
Me.Hide
End Sub
If the Sub is not in the Code Module of the Form you will refer to the Form Object using the Form Name.
Private Sub CommandButton4_Click()
UserForm1.Hide
End Sub
Refer to the MS Excel
VB Help for the: "Hide Method", Hides an object but doesn't unload it.