Making nouns plural in the French language can be a bit more complicated than English, but perhaps not.  Just like in English, you normally add an -s to the written form of the singular.  I say written form, because usually the pronunciation doesn’t change one bit when using a plural noun, except for the links from the article to the noun.  But, just as in English, there are exceptions, of course.

→ Nouns that end in -s, -z, -x do not change in the plural form.
un fils → des fils
un gaz → des gaz
une voix → des voix

→ Nouns that end in -eau, -au, -eu take on an -x in the plural.
un tableau → des tableaux
un tuyau → des tuyaux
un jeu → des jeux
Careful!!!  There are some exceptions to this rule.  un pneu → des pneus

→ There are seven nouns that end in -ou which take on an –x in the plural.
un bijou  → des bijoux
un caillou → des cailloux
un chou → des choux
un genou →des genoux
un hibou →des hiboux
un joujou → des joujoux
un pou → des poux

→ Some nouns that end in -ail or -al take on -aux in the plural.
un travail → des travaux
un corail → des coraux
un émail → des émaux
un vitrail → des vitraux
un animal → des animaux
un journal → des journaux
un cheval → des chevaux
un hôpital → des hôpitaux

→ Others, however, follow the general add an -s rule.  For example:
un bal → des bals
un carnaval → des carnavals
un festival → des festivals

→ There are of course irregular plurals.
un œil → des yeux
un jeune homme → des jeunes gens
un monsieur → des messieurs
une madame → des mesdames
une mademoiselle → des mesdemoiselles
un ciel → des cieux

→ Proper nouns do not change in the plural.  Only the article does:
les Goldman, les Roi, les Fabre.

→ However, an –s can be added to names of artists to when referring to their work.  For example: un Monet → deux Monets (in other words, two Monet paintings).

→ Some nouns are only used in the plural form.  Examples:
les environs, les gens, les mœurs, les vacances (holidays)

Finally, compound nouns have all sorts of different rules, so we’ll leave them for another article.
Till then, Bonne soirée (Have a good evening).