This could be translated as "went up to the town of Bethlehem in Judea." Bethlehem was higher in elevation than Nazareth.
## city of David ##
<b>city of David <b>- Bethlehem was called a city because of its importance, not its size. King David was born there and there was a prophecy that the Messiah would be born there. "City of David" could be translated as "city of King David."
## to register ##
This could be translated as "to have his name written in the register" or "to be included in the count."
## along with Mary ##
Mary traveled with Joseph from Nazareth. It is likely that women were also taxed, so Mary would have needed to travel and be registered as well.
## who was engaged to him ##
This could be translated as "his fiancée" or "who was promised to him." An engaged couple was considered legally married, but there would not have been physical intimacy between them.