first time paris trip!

i'm arriving at orly on the 17th at 23:00, i was wondering what's the best transportation option to go to the city at that time? since it's my first time i was wondering if anyone can recommend places to go to (touristic and not) and must haves for food!! i'm staying for 4 days but sightseeing for two, so i want to be able to see the most remarkable areas and attractions. thanks!!!!