French agreement has nothing to do with opinions; it’s a grammatical function of the language. Just as verbs change to agree with their subjects in most languages (“I am” vs “you are”), so too do adjectives and pronouns in French: they change to agree in gender and number with whatever word they modify or replace (un homme fort vs une femme forte).
Demonstrative adjectives (this, that) are used to indicate a specific noun or nouns. In French, they must agree with the noun(s) in number and sometimes gender: ce, cette, cet, ces.
Indefinite pronouns are vague - they either refer to unspecific nouns (like un autre and quelque chose) or make sweeping generalizations (on, tout le monde).
Most French adjectives have to agree with their nouns in gender and number, but there are many exceptions, known as invariable adjectives. These have just one unchanging form no matter the gender and number of the noun they modify.
Magnetic poetry is a fun little tool you can use to learn and practice French. 500 magnets with words and parts of words help you to express yourself in a unique and creative way.
Multiplicative numbers are, unsurprisingly, words used to multiply nouns. The numbers themselves can be adjectives or nouns - either way, their gender agrees with the nouns they modify / replace.
Every country and continent has an adjective that can be used to describe people and things from that place. Those same adjectives can also be used as nouns to refer to people from that place, with one small change in French.