This is the 129th most frequent French word.
savoir
To know (knowledge or information).
Here, 'savoir' is used to express knowing how to do something.
Je sais jouer du piano.
I know how to play the piano.
In this case, 'savoir' is employed to inquire knowledge of specific information.
Sais-tu à quelle heure part le train?
Do you know what time the train leaves?
Here, 'savoir' is used in a negative form to indicate the absence of knowledge regarding information.