les pronoms indéfinis

A pronoun replaces a noun which has been mentioned or is obvious from context. An indefinite pronoun refers to people or things without identifying them precisely.

quelqu'un, quelque chose

Quelqu'un (somebody) is used in affirmative or interrogative sentences to refer to a person, whether male or female. 

Quelque chose (something) is the equivalent pronoun used to refer to a thing. 

If quelqu'un or quelque chose is followed by an adjective, the adjective needs to be preceded by de. 

The negative form of quelqu'un is personne (no one, nobody) and the negative form of quelque chose is rien (nothing). Remember that ne precedes the verb when personne and rien are used in negative sentences. 

Quelques-uns (a few, masculine) and quelques-unes (a few, feminine) are pronouns used in the plural to speak about people or things. Note that the s at the end of quelques is pronounced before the following uns or unes.

chacun vs. aucun

Chacun (each one) is singular and masculine, chacune is singular and feminine. Chaque, on the other hand, is an indefinite determiner used to modify a noun.

The negative form of chacun is aucun. Aucun (none, not a one, not a single) is singular and masculine, aucune is singular and feminine. They are used with ne.

Aucun des états des États-Unis commence avec Z. None of the states in the US starts with Z.

Autre is always preceded by a determiner: un autre (another, masculine), l'autre (the other, masculine or feminine); une autre (another, feminine); d'autres (others, masculine or feminine), les autres (the others, masculine or feminine)

Note the following phrases with autre: autre chose (something else), l'un et l'autre (the one and the other, both, masc), l'une et l'autre (the one and the other, both, fem), les uns et les autres (one and every, masc), les unes et les autres (one and every, fem), ni l'un ni l'autre (neither one nor the other), l'un à l'autre (to one another), l'un pour l'autre (for one another).