In the Spanish language, what do direct objects (lo, la, los, and las) "tell" in a sentence?
Well, this is a very interesting question. It is vitally important for those of us who speak English as our first language to realise that Romance languages (Italian, French and Spanish etc.) are very different in lots of ways, but one of them is the way that objects have a gender: they are either masculine of feminine. Thus the direct objects that you have mentioned, and also the indirect objects that you haven't mentioned (uno, una, unos, unas) play an important role because they need to match up with the gender of the noun.
For example, we need to say: "La plaza esta en el centro de la cuidad." Note here how "La" goes with "plaza" and "el" goes with "centro" as "plaza" is feminine and "centro" is masculine. Making sure that the genders are matched this way is an important aspect of mastering this language.
The direct object pronouns "lo, la, los, and las" are commonly used in Spanish. In Spanish, they answer "who or what the verb is being done to." For example, take the sentence "Pablo va a tirar la pelota." The direct object is "la pelota." The verb "tirar" or throw is being done to the "pelota" or ball. The direct object pronouns "lo,la, los, and las" replace the entire noun. Thus, if we rewrite the above sentence using a pronoun, it would read "Pablo la va a tirar." Instead of "Pablo is going to throw the ball," we are now saying "Pablo is going to throw it."
There are four different direct object pronouns, as in Spanish it is important that pronouns match nouns in gender and number.
Here are some other examples of sentences rewritten using direct object pronouns:
1. Pablo quiere comer la torta. / Pablo la quiere comer. (Here, we use the direct object pronoun la, to represent "la torta" because it is feminine and singular).
2. Terra cocina los pollos./ Terra los cocina. (Here, we use the direct pronouns los, to represent "los pollos" because it is masculine and plural).