The article lo - Easy Learning Grammar Spanish

Unlike the other Spanish articles, and articles in English, lo is NOT used with a noun.
lo can be used with a masculine singular adjective or past participle (the -ado and -ido forms of regular verbs) to form a noun.

Lo único que no me gusta ...	The only thing I don’t like ...
Esto es lo importante.	That’s the important thing.
Lo bueno de eso es que …	The good thing about it is that …
Sentimos mucho lo ocurrido.	We are very sorry about what happened.

For more information on the Past participle, see The perfect tense.

lo is also used in a number of very common phrases:

•	a lo mejor	maybe, perhaps
	A lo mejor ha salido.	Perhaps he’s gone out.

•	por lo menos	at least
	Hubo por lo menos cincuenta heridos.	At least fifty people were injured.

•	por lo general	generally
	Por lo general me acuesto temprano.	I generally go to bed early.

lo can also be used with que to make lo que (meaning what).

Vi lo que pasó.	I saw what happened.
Lo que más me gusta es nadar.	What I like best is swimming.

Grammar Extra!lo can be used with de followed by a noun phrase to refer back to something the speaker and listener both know about.

Lo de tu hermano me preocupa mucho.	That business with your brother worries me a lot.
Lo de ayer es mejor que lo olvides.	It would be best to forget what happened yesterday.

lo can be used with an adjective followed by que to emphasize how big/small/beautiful and so on something is or was. The adjective must agree with the noun it describes.

No sabíamos lo pequeña que era la casa.	We didn’t know how small the house was.
No te imaginas lo simpáticos que son.	You can’t imagine how nice they are.