PLURALS OF NOUNS
Most nouns in French form their plurals by adding "s". So we have "le livre" and "les livres", "la table" and "les tables", as you know from Articles 02.
However, some words in French add an "x" instead of an "s". Generally these words end in "u" or sometimes "l". We'll look at the "-u" words first (and the "-l" words on Nouns 03).
There are a couple of 'exceptions (aren't there always!) like "le trou" (hole) and "les trous", "le pneu" (tyre) and "les pneus", but the common "-u" words that add "x" in the plural are shown below.