Pronoun-a word that can function by itself as a noun phrase and that refers either to the participants in the discourse (ex.i,you ) or to someone or something mentioned elsewhere in the discourse (ex.she,it,this).
a word or phrase that modifies or qualifies an adjective, verb, or other adverb or a word group, expressing a relation of place, time, circumstance, manner, cause, degree, etc. (ex.Gently,quiet,there ).
a word or phrase naming an attribute, added to or grammatically related to a noun to modify or describe it.
a word used to connect clauses or sentences or to coordinate words in the same clause (ex.but,if).
a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause, as in “the man on the platform,” “she arrived after dinner,” “what did you do it for ?”
an exclamation, especially as a part of speech, e.g., ah! or dear me!.

Your Welcome =)
They are all parts of speech.
Pronoun is used to replace a name of a noun or another pronoun.
Adverb is used to modify verb, adjective and adverb.
Adjective is used to modify nouns and pronouns.
Conjunction are words used to connect clauses, phrases,words or sentences.
Prepositions is used in a sentence to locate place and time.
Interjection is used to show and express a particular emotion or sentiment.