The verbs sapere and conoscere both mean "to know," but have different implications. Sapere means "to know," "to be able to," or "to know how to." Take a look at these examples with the io form of sapere:

So la lezione. (I know the lesson.)

So cantare. (I know how to sing. I am able to sing.)

Conoscere means to know, to be acquainted with, or to make the acquaintance of:

Io conosco Francesca a casa di Giuseppe. (I met Francesca at Giuseppe