De cual libro estas hablando?
Una persona que 'nada bien' es una persona que tiene la habilidad y destreza para nadar en el agua.
A person who 'nada bien' is a person who has the ability and skill to swim in the water.
You use saber to describe a fact, information, or how to do something.
And you use conocer to say that you are familiar with something either a person, place, or thing.
Basically saber means to know of something, and conocer means to be familiar with someting.
