How do I know when to use saber or conocer?

A common mistake made amongst all learners of Spanish but with a little practice it can be easily avoided.

saber - to know a fact/thing/skill

'Ella sabe muchos idiomas' = She knows many languages

'Yo sé hacer matemáticas' = I know how to do maths.

Be careful with saber as it is an irregular verb, which means the conjugation doesn't follow the normal pattern of -er verbs. E.g. 'Yo sé.'

conocer- to know someone or be familiar with someone/something

'Mi padre conozca a mi amigo.' = My father knows/is acquainted with my friend.

'Yo conozco la Sagrada Familia'.= I know the Sagrada Familia.

Conocer is also a difficult verb conjugation as a 'z' is added in conjugation with the 1st person singular (I), the 3rd person singular (he,she, it) and the 3rd person plural (they).