Subject pronouns indicate who or what is performing the action of a verb. There are a total of six grammatical persons, each of which has at least one subject pronoun.
You probably know the expressions mon cher et ma chérie, but French has many more interesting ways to refer to their dears and darlings - mostly terms related to food and animals.
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.
L'accent circonflexe va disparaître des manuels scolaires à la rentrée - que s'est-il passé, et qu'en pense le ministre de l'Éducation nationale Najat Vallaud Belkacem ?
The subjunctive conjugations for many otherwise irregular verbs are regular, but not all. Stem-changing verbs and what I like to call very irregular verbs have irregular subjunctive conjugations.