Why do you need a macro for this? Select the word and click CTRL+K. The word will be the text of the hyperlink. You just need to add the address.
If you need a macro then you need something like the following which will replace the selected text with the named link.
Sub AddLink()
Dim oRng As Object
Dim oLink As Object
Dim strLinkText As String
Const strLink As String = "https://www.fedex.com/apps/fedextrack/" 'the link
On Error GoTo ErrHandler
If TypeName(ActiveWindow) = "Inspector" Then
If ActiveInspector.IsWordMail And ActiveInspector.EditorType = olEditorWord Then
Set oRng = ActiveInspector.WordEditor.Application.Selection.Range
strLinkText = Trim(oRng.Text)
Set oLink = oRng.hyperlinks.Add(Anchor:=oRng, _
Address:=strLink & strLinkText, _
SubAddress:="", _
ScreenTip:="", _
TextToDisplay:=strLinkText)
Set oRng = oLink.Range
oRng.collapse 0
oRng.Select
End If
End If
lbl_Exit:
Set oRng = Nothing
Set oLink = Nothing
Exit Sub
ErrHandler:
Beep
Err.Clear
GoTo lbl_Exit