B is for backstory. It's often necessary to look into the past of your characters. It helps explain to the reader the kind of person your character is. Maybe they had a traumatic childhood that led them to be the devious villain they now portray in your story. Sometimes you need to delve into the distant past for world building purposes. It helps explain the world politics, how things came to be, etc. Sometimes you need only go back a short ways, explain what happened a few days prior so you know why that character is in the position they are now. Back story isn't always necessary, but I think it helps your characters and world be a bit more three dimensional and believable. Besides, it makes for good story telling.
Day 2: Did you hit your first word goal? Behind already? DO.NOT.PANIC! You'll find there will be days when you'll easily surpass the suggested 1,667 daily word counts and sometimes you'll fall short. Don't let it get to you. I know someone who wrote 30k words in the last three days to win. You can do it!