Definite article and units of measurements

The definite article is used before units of weight or measure in Spanish where the indefinite article is required in English.

Estas manzanas cuestas 12 pesos el kilo.

These apples cost 12 pesos a kilo.

Definite article and parts of the body

The definite article is used with parts of the body and clothing instead of the possessive pronouns.

Debes ponerte el impermeable cuando está lloviendo. 

You should put on your raincoat when it's raining. 

Nos lavamos la cara. 

We washed our face. 

Los estudiantes levantaron la mano. 

The students raised their hands. 

Definite article in days of the week

The definite article is used before names of the days of the week instead of en to translate the English "on".

Llegarán el viernes. 

They'll arrive on Friday.

Van a la iglesia los domingos. 

They go to church on Sundays. 

The article is not in used after any form of the verb ser. 

Hoy es domingo. 

Today is Sunday. 

Ayer fue sábado. 

Yesterday was Saturday.