Questions about nouns
Q: Why is it des chevaux and NOT des chevals?
Most nouns that end in -al form their plural with -aux.
Q: Why is it des arcs-en-ciel and NOT des arcs-en-ciels?
If two nouns in a compound are separated by a preposition, only the first noun has a plural marker.
Q: Why is it j'ai lu un livre and NOT j'ai lu une livre?
The word for "book" is un livre (une livre means "a pound").
Q: Why is it chez les Tremblay and NOT chez les Tremblays?
Family names don't have a plural marker.
Q: Why is it j'aime l'emplacement and NOT j'aime la location?
The French word location means "rental" (from the verb louer). To express this in French, use emplacement, lieu or a structure with où ...
Q: Why is it j'ai fait une demande d'emploi and NOT j'ai fait une application d'emploi ?
The French word application refers to applying a substance (e.g.: a liquid, like paint) to an object; it can also mean "attention/concentration" (par ex.: travailler avec application). It can't be used though when refering to a form or job.
Q: What is the difference between an and année?
They both mean "year". The word année focuses on the duration and tends to be used with the word pendant and non-numeric adjectives like toute, bonne, difficile, meilleure and pire, e.g.: une année difficile, toute l'année. On the other hand, the word an tends to be used with numbers, e.g.: l'enfant a un an et demi, un voyage de trois ans.