You can address many different objects (words, paragraphs, headers etc)
in Word and you can modify each addressed object as
described below. You do not have to go about like the old versions where
you first would have to go to/select the object to modify before you could
make any changes to it.
ActiveDocument.Words(1).Text = "FirstWord1"
ActiveDocument.Paragraphs(1).Range.Text = "My first paragraph's text."
"Text in the header"
ActiveDocument.Tables(1).Columns(3).Cells(1).Range.Text = "whatever"
Where possible avoid using the Selection object. It is considered
faster running code with the method described above.