On this Sunday, the 'Vigil of the Nativity' is the Mass offered when using the 1962 calendar for all Masses offered before First Vespers of Christmas i.e. all day on Christmas Eve.
The Vigil of the Nativity takes the place of the IV Sunday of Advent, which is supressed this year. However, those who recite the Breviarium Romanum would say First Vespers of the IV Sunday of Advent as the 'Vigil of the Nativity' does not have any First Vespers!
This Mass is not the First Mass of Christmas (e.g. Midnight Masss) and neither does it fulfil the obligation to attend one of the three Nativity Masses (Midnight/Dawn/During the Day).