Prepositions
Prepositions are words which link two related parts of a sentence.
They are placed in front of nouns in order to indicate a relations.ip between that noun and the verb, adjective, or noun that precedes it.
use of prepositions with place-names
contractions with a and de with la and les

à (at)
de (of)
en (in)

avant and arrière are prepositions and therefore do not agree with nouns
droit and gauche are regular adjectives that do agree

prepositions and articles
Féminins (en, de)
Masculins (au, du, dans le)
la, le, l’

Moi Mots
Elements of Grammar