Spanish indefinite articles

Spanish indefinite articles refer to one individual out of a general group and they often correspond to English a / an (singular form), some / a few (plural form). Like definite articles, they give information about the gender (femenine, masculine) and the number (singular, plural) of the noun and they have four forms: 

Examples: 

• Miguel quiere comprar un libro. (Miguel wants to buy a book.)
• Acabamos de recibir una carta. (We have just received a letter.)
• Necesito comprar unos tomates para la cena de esta noche. (I need to buy some tomatoes for tonight's dinner.)
• Pon unos vasos encima de la mesa. (Put a few glasses on the table.)

When to use the indefinite article in Spanish 

Like English, the Spanish indefinite article is used in the following cases: 

When referring one individual in a general group

Un cuadro es una obra de arte. (A painting is a work of art.)

When describing someone with a noun

Gracias, eres un sol. (Thanks, you are a sweetie.)

When saying there is exactly one of something 

Quiero una galleta. (I want a biscuit.)

When describing an approximate amount of something 

Necesito unos calabacines. (I need some courgettes.)

When to omit the indefinite article in Spanish

The indefinite article has to be omitted in the following cases: 

With non specific amount of material 

¿Pones zanahorias en la tarta? (Do you put any carrot in the cake?)

With ser + professions and occupations, nationality or religion

• Somos albañiles. (We are bricklayers.)
• Somos españoles. (We are Spanish.)
• Yonis es musulmán. (Yonis is Muslim.)

If the noun is modified by an adjective, the indefinite article cannot be omitted.

       Example:

       Javier es un profesor muy competente. (Javier is a very competent professor.)

With cierto(a) / medio(a) / mil / otro(a) / qué / tal(-es) + noun

• Cierto día decidieron que lo mejor era terminar su relación. (They decided one day that the best thing to do was end their relationship.)
• José y Lorena van a salir en media hora. (José y Lorena are leaving in a half hour.)
• Perdieron mil euros en la apuesta. (They lost one thousand euros on the bet.)
• Quiero comprame otra bicicleta. (I want to buy another bike.)
• Miguel, ¡Qué bonita novia tienes! (Miguel, what a beautiful girlfriend you have!)
• No quiero escuchar tal cosa. (I don't want to listen to such a thing.)

With verbs such as tener / comprar / sacar / buscar / llevar 

The indefinite article is omitted after verbs such as: 

• tener (to have);
• comprar (to buy);
• sacar (take off / get)
• buscar (to look for);
• llevar (to bring)

when the noun refers to a person or thing one commonly have.

Examples: 

• Lorena tiene marido. (Lorena has a husband.)
• Me estan buscando novia. (They are looking for a girlfriend for me.)
• Lleva zapatos. (She is wearing shoes.)
• Miguel ha comprado (sacado) billetes. (Miguel bought the tickets)