Use la (and el, las, los) before nouns to:
* identify something specific
* refer to something that has already been mentioned
* refer to something that is unique
* say how often you do something
* indicate an amount of something when we’re talking about time/money
Use la/el etc before a noun which is specific
El profesor está dando clase.
The teacher is giving a class.
María está leyendo la carta.
María is reading the letter.
When you are referring to something that has already been mentioned
¿Tienes hijos? - Sí, tengo dos hijas.
Do you have children? - Yes, I have two daughters.
La ciudad de Barcelona es muy bonita.
The city of Barcelona is very beautiful.
When you are referring to something which is unique
María está escribiendo una carta a su madre.
María is writing a letter to her mother.
La Torre Eiffel es un monumento muy famoso.
The Eiffel Tower is a very famous monument.
To say how often you do something
Tomo el autobús al trabajo todos los días.
I take the bus to work every day.
Vemos la tele todas las noches.
We watch TV every night.
When you are talking about time/money
Ella trabaja diez horas al día.
She works ten hours a day.
El billete cuesta cien euros.
The ticket costs one hundred euros.