npm-star man page
npm-star — Mark your favorite packages
npm star [<pkg>...] npm unstar [<pkg>...]
"Starring" a package means that you have some interest in it. It's a vaguely positive way to show that you care.
"Unstarring" is the same thing, but in reverse.
It's a boolean thing. Starring repeatedly has no additional effect.
npm help view
npm help whoami
npm help adduser