It depends. If you hear someone asking "¿Lo qué?", that´s a very informal way of saying "what?" in Spain. But generally they´re just pronouns. You could use it for example like this: LO QUE me dijiste es mentira: WHAT you said was a lie.

Generally, "lo que" serves as a relative pronoun and translates to "that" or "which" in English. However, I find it useful to think of "lo que" as having the literal meaning "that which". Of course, you would never say "that which" in English but, for me anyways, thinking of it that way helps me use it in the right way in Spanish. Here's what someone else wrote on spanishdict.com http://www.spanishdict.com/answers/109139/lo-que-vs-qu I would translate "lo que" as "what" (as in an object or idea) "Te dijo lo que estaba pensando" He told you what he was thinking, the "What" being "whatever it was". If you said "te dijo que estaba pensando" it would mean "he told you that he was thinking" So therefore I would translate "que" (when used in the middle of a sentence, like so) as "that". Examples: "Yo sé que tu quieres ir al banco" - I know that you want to go to the bank "Yo sé lo que quieres hacer" - I know what you want to do. "Me dices que estás pensando" - You tell me that you are thinking. "Me dices lo que estás pensando" - You tell me what you are thinking.