The neuter article "lo" has no direct translation in English, but it is widely used. It has only one form (does not change depending on gender or number), and it is used as follows:

With adjectives (lo + adj. + que):

Mira lo hermosa que eres. (Look how beautiful you are.) Mira lo contento que está.  (Look how happy he is.) Mira lo ambicioso que es. (Look how ambitious he is.)

The article "lo" stresses the quality of the adjective it describes. In some cases it may be substituted by an abstract noun, but the meaning may change a bit: Mira lo hermosa que eres. (Look how beautiful you are.) Mira tu hermosura. (Look at your beauty.) Mira lo contento que está.  (Look how happy he is.) Mira su felicidad.  (Look at his happiness.) Mira lo ambicioso que es. (Look how ambitious he is.) Mira su ambición. (look at his ambition.)

Notice what happens when we change an adjective for a noun: Lo alto del edificio. (The highest part of the building.) La altura del edificio. (The height of the building.)

With adverbs (lo + adv. + que):

Fíjate lo bien que escribe. ( Look how well he writes.) ¿Ves lo mal que conduce?  (See how badly he drives?) ¿Puedes creer lo lento que vamos?  (Can you believe how slowly we move?) Él ve solamente lo malo. (He only sees what is bad.)

Note that "lo" may also be used in an exclamatory sense: ¡Mira lo bien que vive!  ( How well he lives!) ¡Escucha lo bien que canta Juan!  (Listen to how well Juan sings!)

With participles:

Lo prohibido gusta más. (What is forbidden is most pleasurable.) Lo pasado, pisado (What is past is forgotten.) "Lo" also appears in the following idiomatic expressions: Juan hace todo a lo grande. (Juan does everything on a grand scale.) Carlos conduce a lo bestia.  (Carlos drives in an extreme fashion.) Después de todo, me da lo mismo.  (After all, it’s all the same to me.) Es lo de siempre.  (It’s always the same thing.) Eso es lo de menos. ( That’s what matters least.)

With possessive adjectives:

Quiero que me des lo mío.  (I want you to give me what is mine.) It is also used with other elements that function as adjectives: ¿Supiste lo de Juan? (Did you know that thing about Juan?) ¿Te enteraste lo que pasó el otro día?  (Did you find out about what happened the other day?)

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