Basically everything or at least a whole lot

.
A macro is a named sequence of statements executed as a unit. For
example the I use the following AutoOpen macro to ensure that every
document I open in Word opens in the view that I want and with several
annoying toolbars turned off:
Sub AutoOpen()
ActiveWindow.Caption = ActiveDocument.FullName
With ActiveWindow.View
..Type = wdPrintView
..Zoom.PageFit = wdPageFitBestFit
..FieldShading = wdFieldShadingAlways
End With
With CommandBars
..Item("Reviewing").Visible = False
..Item("Mail Merge").Visible = False
..Item("Forms").Visible = False
End With
End Sub
In Microsoft Word, a style is a collection of formatting instructions.
You might apply the builtin "Title" style to title all of your papers
with Arial 16PT font centerd between the margins. See:
http://www.shaunakelly.com/word/styles/TipsOnStyles.html
You can apply a style with a macro e.g.,
Sub ApplyBodyTextStyleToSelection()
Selection.Range.Style = wdStyleBodyText
End Sub
You can't apply a macro with a style.