When should I use au, à la, à l' and aux?

First of all, it is important to understand the meaning we are trying to convey. Au, à la, à l' and aux are all ways of saying 'to the' or 'at the'. For example, in order to say 'I work at the cinema' in French, we would say 'je travaille au cinéma'. We use the different variants au, à la, à l' and aux depending on the gender and number of the noun which follows. For instance, we said 'je travaille au cinéma' because cinéma is a masculine noun. For a feminine noun, like 'maison', we would use 'à la' : 'il est resté à la maison'. For a singular noun which begins with either a noun or 'h', we would use 'à l''. An example of this is the sentence 'je vais parler à l'ami de Pierre'. Finally, for plural nouns we use 'aux' : 'j'habite aux États-Unis.