Good afternoon jts2004
You will need to design a userform (go to Insert > Userform from the VBE) which is simplicity itself and use this call to show it (assuming you name it UserForm1):
Userform1.Show
and to dismiss it:
Unload UserForm1
A MsgBox wouldn't be suitable in this instance as it needs user intervention to be closed.
HTH
DominicB