Passing selected data from multi select list box to text box.

Try this...

Private Sub CommandButton1_Click()
    Dim i As Long, MyString As String
    
    With ListBox1
        For i = 0 To .ListCount - 1
            If .Selected(i) Then MyString = MyString & IIf(MyString = "", "", ", ") & .List(i)
        Next i
    End With
    Me.TextBox1.Text = MyString
End Sub