Deirdre and George are getting married in the village of Yarmouthport, which is near Hyannis. Hyannis is accessible by land, sea, and air, with land being the most common and least expensive choice for most.
Air: Most people who fly to Cape Cod actually fly into Boston's Logan Airport and either drive or take a bus to Cape Cod. There is a small plane commuter service into Hyannis, but the costs are often prohibitive. Hyannis is less than 90 minutes for Boston's airport by car and there is a REALLY convenient bus service that picks up at the terminal and delivers one to Downtown Hyannis. There are also the usual Car Rental options.
Land: Hyannis is less than 90 minutes from Boston. Link to google maps to find your way.
Sea: This was a bit of a joke, unless you plan to spend time in Nantucket or Martha's Vineyard prior to the wedding. That said, both Nantucket and Martha's Vineyard are beautiful and shouIf that is that case, you can take a ferry from both of those islands into Hyannis.