Uses of la,le and lo?
For some reason I just cannot seem to get the meaning of these certain words! I do pretty well at reading Spanish until I come upon "lo" and then I get confused. For example, there's a song that I listen to and one line says "Eres, lo que quiero mas en este mundo eso eres" I get it pretty well until I see the "lo". Can someone please explain to me why the "lo" is put into sentences and explain what it means or why you have to put it there? It would help me so much! Muchas gracias! 
1 Answer
Lo has several uses. Here are the ones that come to mind:
Lo is a direct object pronoun referring to masculine inanimate, objects (it) or to male persons (him).
Allí está el libro. Démelo. Here the word is "it" referring to the masculine word, book.
There is the book. Give it to me.
Acállelo. Silence him. (shut him up)
Lo is also a neuter form of the definite article used with adjectives functioning as nouns.
Lo mejor sería que..... Since adjectives don't have gender, when one is used as a noun the neuter lo definite article is used.
The best thing would be that....
In your example the lo is part of the relative pronoun lo que (el que, la que, el cual, lo cual, la cual, los que, las que, etc.)
Again, the lo (neuter form) is used to refer to abstract or unknown nouns, concepts, etc. where we don't know the gender (el que or la que) to assign to it.
Eres, lo que quiero mas en este mundo. Eso eres.
You are (that which, the thing that) I want most in this world. You are that thing.
I used that thing or that which, rather than whom or the one, because if it was referring to you as a person we would know the gender and la que would most likely be used).
Eres, la que quiero más en este mundo. Esa eres.
You are the one that ( whom) I love the most in this world. You are that one.
There are probably other uses for the word lo, but these are among the most common one.
