1. "un" and "une" are both indefinite articles. In English, it is "a". Just like you say "a dog" in English, it is "un chien" in French. In English, there is only one version of "a" but in French, there are 2 versions. One is for masculine words "un" and the other for feminine words "une". There is no way to know which word is feminine unless it concerns a female, as in "girl". If you say "a girl" then you know for certain that it will be "une" - "une fille". Other than that, you need to learn each article for each noun. There is no rule. 2. It's the same as above. "Le" is masculine while "la" is feminine. In English, it is "the", a definite article. "The girl" - "la fille" and "the dog" - "le chien". As for "l'" - that happens when the noun is starting with a vowel. If you have a word such as "l'école" - "the school" then it is actually "la école" but in French, you don't let those vowels clash like that, that's why you remove the "a" in "la" and replace it with an apostrophe. However, you have to go by sound. There are words like "l'hôpital" - "the hospital" which don't start with a vowel but the "h" in "hôpital" is silent which is why you remove the "a" in "la" as well - "l'hôpital". I hope this was helpful.