As far as my understanding goes, "les" is used to describe a direct object of the verb, like in this exercise which is referring to "them" directly, meaning the action of the verb is used on them. In comparison, "leur" is used for expressing that the verb is used on an object involving them. For more information try http://french.about.com/od/grammar/a/pronouns.htm
Can anyone tell me how in the heck I can tell between plural and singular. For instance: Je les connais - They pronounce it: Je le cone (the way it sound to me) and to my sweet ears that is singular, they eat the S and every time I loose a heart because I can never tell when it is plural. For instance, in spanish you will hear it like this: Je les conne but in french it sounds Je le cone, NO S Help me please.
You can tell it is plural since "les" is pronounced different from "le" – not in the "s", but in the "e". The e in les is pronounced similar to the e in "end", while the e in le is pronounced (kind of) similar to the e in "Earl". Probably best to listen to this (hold the mouse button over the word in Duolingo) since it might vary depending on the English accent..
I understand connaître to mean "know" in the sense of "to be familiar with", not just "to have knowledge of". So in view of that, I answered "I am familiar with them" and got it wrong. I don't see how my answer is wrong when connaître is a broader kind of knowing than just knowing the fact that someone or something is.
"les" doesn't mean "it". Depending on the gender of the noun, the direct object of "it" translates to either "le" or "la".
My friend has a car and I see it - Mon ami a une voiture et je la vois. ("voiture" is feminine, so "la" is used)
She wants the butter, but her brother hides it - Elle veut le beurre mais son frère le cache. ("beurre" is masculine, so "le" is used)
Hence that "le" also means "him" and "la" also means "her", but you get which one is being used due to the context of the sentence.
Je le connais - I know him
Je la connais - I know her
"savoir" is used for facts (I know she has a sister - je sais qu'elle a une sœur).
"connaître" is used for persons or places (my brother's friend knows my mother - le ami de mon frère connaît ma mère).