Sandbox, you point and click doors, hallways, etc. With choices. VN, is like you reading a book, well watch it, having choices (in some games, some are kinetic which means no choices), and it plays out like one long movie/TV show.
Surely, you've played some games on site tagged with "VN" and also some that have tags with sandbox. Sandbox is basically repeating things over and over to some extent, VN plays scenes one thing after another.
As with sandbox you have some pointing and clicking to do to decide your next place you want to go, well some games give that freedom while others are kind of linear.