One of the eight parts of speech, adjectives are a type of modifier. They serve the same purpose in French and English, but they are very different in two respects.
Most French verbs are conjugated with avoir as their auxiliary verb in compound tenses and moods, and therefore do not require agreement with their subjects. But avoir verbs do need agreement in a very specific construction: the past participle must agree with the direct object when it precedes the verb.
All pronominal verbs are être verbs in compound tenses and moods like the passé composé, which means that the past participles must agree with their subjects - at least in theory. In fact, it's not quite so straightforward.
The three French verb constructions which include some form of être plus a past participle usually require grammatical agreement of the past participle with the subject.
Verbs of perception are subject to grammatical agreement in the compound tenses, but the rules are somewhat tricky - they only agree with their subjects when they precede the verb.
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.
Certain aspects of French grammar are a bit different with the causative than with other two-verb constructions.
The French definite article (le, la, l', les) indicates either a particular noun or, contrarily, the general sense of a noun. It's used similarly to its English counterpart, but there are many instances where a definite article is required in French but not English.
Indefinite pronouns are vague - they either refer to unspecific nouns (like un autre and quelque chose) or make sweeping generalizations (on, tout le monde).
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.
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.
The indefinite French subject pronoun on literally means "one," but is usually translated by an indefinite subject. Agreement with the subject implied by on is optional - at least in theory.