Bucharest has just two points of entry: Otopeni (Henri Coanda) Airport and Gara de Nord train station. All international and internal flights to and from Bucharest land at and take off from Otopeni, while all international (and most local) trains arrive and depart from Gara de Nord.
Otopeni is a 30-45 minute drive north of the city (it depends on traffic) while Gara de Nord is just a few minutes from the city centre.