To get a bus to Hendon (Thameslink) station, click Hendon Town Hall bus stop.
Northern Line tube trains run from Hendon Central station.
There are placed out of London you can use Oyster but many lines where Oyster is not valid beyond a certain station. If you go to far you may get fined. So use this map to see where you can and cannot go. It also shows the more expensive national rail lines and the cheaper tube routes.