An article is a word that modifies a noun in a particular way, by stating whether the noun is specific, unspecific, or partial. There are three types of French articles, and they all agree in gender and number with the nouns they modify.
Learn the basics of nouns and pronouns in the first edition of Grammar without Grief, an animated introduction to grammar essentials.
Adjectives comprise one of the eight French parts of speech, but certain members of other grammatical categories can sometimes be used as adjectives. These "non-adjectives" are invariable: there's no gender/number agreement with the nouns they modify.
One of the eight parts of speech, a noun is commonly defined as "a person, place, or thing." If that seems vague, that's because it is.
Most French nouns and adjectives become feminine with the addition of e, but there are some exceptions. Some nouns require an additional spelling change, depending on the final letter(s) of the word.
Most French nouns and adjectives become plural with the addition of s, but of course there are exceptions.
When used as a noun or adjective, the present participle follows the same agreement rules as other nouns and adjectives, and some verbs have a different present participle conjugation for these usages.