1. You can’t go to the movies tonight because tomorrow is a school day, you’re supposed to be saving your money, and you just went to the movies last night. Now, if you want it in a nutshell, the answer is no.
2. We’re eager to find out what her plans are. Tell us in a nutshell: is she going or not?

Compare to: long and short of it; nitty gritty; bottom line. The expression suggests that the words are so few that they can fit in a nutshell.