Here, in rough order of how common they are, are the ways that lo can be used:
As a masculine direct-object pronoun: In such cases, lo can be translated as either "him" or "it." The feminine equivalent is la.
- ¿Pablo? No lo vi. Pablo? I didn't see him.
- El coche es muy caro. Quiero comprarlo. The car is very expensive. I want to buy it.
- Dámelo. Give it to me.
- No creo que lo hayas conocido. I don't think you've met him.
As a neuter definite article: The definite articles in Spanish, typically el and la when singular, are the equivalent of the English "the." Lo can be used as a neuter definite article before an adjective to make an abstract noun. For example, lo importante can be translated as "the important thing," "that which is important" or "what is important."
- Lo bueno es que hemos sido más listos. The good thing is that we have been more clever.
- Lo barato sale caro. What seems cheap ends up expensive.
- Lo mejor es que me voy a casa. The best thing is that I'm going home.
- Lo mío es tuyo. What is mine is yours.
- El entrenador se especializa en lo imposible. The coach specializes in the impossible.
As a neuter direct-object pronoun: Lo can be used as an object pronoun to refer to something abstract, to an unnamed activity or situation, or to a previous statement:
- No podemos hacerlo. We can't do it.
- No lo comprendo. I don't understand it.
- Mi religión no lo prohibe, pero cada vez que lo hago, le doy las gracias al animal por darme vida. My religion doesn't prohibit it, but every time I do it, I give thanks to the animal for giving me life.
With ser and estar to refer to a preceding noun or adjective: This is especially common when answering questions:
- —¿Es nueva tu computadora?. —No lo es. "Is your computer new?" "It isn't."
- —¿Estaban felices?. —Sí, lo están. "Were they happy?" "Yes, they were."
As part of lo que or lo cual: These phrases serve as relative pronouns usually meaning "that," "what" or "that which":
- (Título) La marihuana: Lo que los padres deben saber. (Headline) Marijuana: What parents ought to know.
- Mis padres me daba todo lo que yo necesitaba. My parents gave me everything that I needed.
- No puedo decidir lo que es mejor. I can't decide what is better.
- No todo lo que brilla es oro. Not everything that shines is gold.
As part of lo de: The phrase can be translated differently depending on the context, but generally means something like "the matter concerning":
- Los senadores republicanos fueron informados sobre lo de la CIA. The Republican senators were informed about the CIA matter.
- Lo de que las niñas japonesas se perdieron no era una mentira. The story about the Japanese girls getting lost wasn't a lie.
- Lo de Castro es todo pretextos y mentiras. Castro's way of doing things is all pretexts and lies.
- a lo largo de, throughout
- a lo lejos, in the distance
- a lo loco, like crazy
- a lo mejor, probably
- lo saber todo, to know it all
- por lo general, generally
- por lo menos, at least
- por lo pronto, for now
- por lo tanto, as a result
- por lo visto, apparently

