I still don't get the difference between la and le...when should I use each one?
Each noun is designated a gender by which it is identified with "le" or "la". One being masculine while the other being feminine, respectively. (Le = masculine, La = feminine) You should memorize each noun with its appropriate definite article, when in doubt, reference an online dictionary if need be. Though there are some patterns (along with exceptions to the patterns) that do occur which may help you. E.g. nouns ending in "-ment" are masculine (except la jument) so, l'argument, l'abaissement, l'abonnement and le classement are all masculine. Reference here for more assistance. http://french.about.com/od/grammar/a/genderpatterns.htm I hope this helps, even a little.
These are the definite articles, le = masc. and la = fem.
LaGueule is correct that you should always learn new nouns with it's article to help learn the genders, but I would recommend using the indefinite articles (UN and UNE) to learn new nouns since sometimes you get some nouns that begin with a vowel. For example: "L'examen" and "L'université". The gender is not readily apparent to beginners that don't know all the patterns. But if you learn these words as "Un examen" and "Une université" then the gender is apparent.