"Le" is the, "un" is a, L' is a simplified form. These words are the articles used on masculin noun. "La" is the, " une"" is a, L' is a simplified form.These words are the articles used on feminin nouns.

Hello Nikki Un, une are indefinite article Le, la, les are definite article. ex : un ballon.... (doesn't matter which one) le ballon ... ( the ball we play with) It is the same difference in english with "a" and "the". Then we use le + masculin noun la + feminin noun l' + feminin or masculin but the word after that start by a vowel or an "h" ex : l'homme (the man) or l'identité (the identity) les + plurial nouns We use un + masculin noun une + feminin noun des + plurial noun.