Four articles, chosen by gender and number
English gets by with a single definite article. Spanish picks one of four, because the article agrees with the noun in gender (masculine or feminine) and number (singular or plural). English nouns have no gender, so learn each noun together with its article: not casa but la casa.
Where the article goes
Known or specific things
El libro está en la mesa.
The book is on the table.
Las llaves están en el coche.
The keys are in the car.
English drops the article when it talks about things in general. Spanish keeps it: not Me gusta café but Me gusta el café. When you hesitate, Spanish almost always wants the article where English leaves it out.
Things in general
Me gusta el café.
I like coffee.
Me gustan los gatos.
I like cats.
Days of the week ("on Monday")
Tengo clase el lunes.
I have class on Monday.
El sábado estoy en casa.
On Saturday I am at home.
