It's used to highlight an important point or a detail that should be paid particular attention to. It's often used in scholarly writing, academic papers, and sometimes in literary texts.
Here's how it's typically used:
* NB: followed by the important point or detail.
* N.B.: followed by the important point or detail.
Example:
"The novel explores themes of love and loss. NB: The protagonist's journey is heavily influenced by her childhood experiences."
In this example, "NB" highlights the significance of the protagonist's childhood in understanding her journey.