Troll through this code. It does more than you want, so you can cut it
down to size.
------------------------------------------------------------------------
---------
Option Explicit
Dim tb_One As Object
Dim All_Valid_YN As Boolean
Dim Input_Path As String
Dim Output_File As String

Private Sub Browse_Output_File_Click()
Output_File = Browse_Select("Output_File")
End Sub
Private Sub Button_Input_Path_Click()
Input_Path = Browse_Select("Input_Path")
End Sub
Private Function Browse_Select(This_File As String)
Dim File_Selected

Select Case This_File
Case "Input_Path"
File_Selected = Application.GetOpenFilename("Excel Files
(*.xls),*.xls", , "Select File from Input Directory")
If File_Selected = False Then Exit Function

' Open the file to get its path
Workbooks.Open filename:=File_Selected, UpdateLinks:=False
File_Selected = ActiveWorkbook.Path
Application.DisplayAlerts = False
ActiveWorkbook.Close
Application.DisplayAlerts = True

Me.tb_Input_Path = File_Selected
Me.tb_Output_File = File_Selected & "\Multiple Mills " &
Application.text(Now(), "yyyymmdd")

Case "Output_File"
File_Selected = _

Application.GetSaveAsFilename(InitialFilename:=Input_Path & "\", _
FileFilter:="Excel files,*.xls", Title:="Select Output
file name")
End Select

If File_Selected = False Then Exit Function

Browse_Select = File_Selected
Me.Controls("tb_" & This_File) = File_Selected
Me.Button_OK.SetFocus
End Function
Private Sub Button_Cancel_Click()
Me.Tag = vbCancel
Me.Hide
End Sub
Private Sub Button_OK_Click()
Range("Input_Path") = Me.tb_Input_Path
Range("Output_File") = Me.tb_Output_File

Me.Tag = vbOK
Me.Hide
End Sub
------------------------------------------------------------------------
---------------------------
Note that all this code  is part of a form, the design of which you can
figure out from the above code. Credit to Sheila Cooksey, Perth for
code.