“des” is the plural of the indefinite articles “un” and “une”. “les” is the plural of the definite article “le” and “la”.
Not all words form their plural by adding an “s”. The plural of a noun depends on its ending as we will see in this lesson and in the ones that will follow.
Nouns ending in “au”, “eau”, “eu” and “oeu”
The nouns ending in “au”, “eau”, “eu” and “oeu” form their plural by adding an “x” to the end of the noun.