A pronoun stands in place of a noun (Latin prōnōmen, for a noun). Latin has several classes of pronoun, and each does a different job: some name the speaker and the person spoken to, some refer back to the subject, some point to something near or far, some link one clause to another, and some ask a question or leave the identity open.
The classes are related in ways that explain much of the system. The personal pronouns ego, tū, nōs and vōs are irregular, and the reflexive sē has no nominative. Latin has no true pronoun of the third person: where English says he, she or it, Latin uses a demonstrative, most often is, ea, id, which is why the demonstratives and the personal pronouns belong together. The possessives meus, tuus, suus, noster and vester are really adjectives and agree with the thing possessed. The relative quī, quae, quod and the interrogative quis, quid are built on the same stem and share most of their forms, and the indefinites such as aliquis, quīdam and quisque are made by adding a prefix or a suffix to that stem.
How the pronouns work in clauses, for example in relative clauses and indirect questions and in indirect speech, is the subject of Syntax. The complete tables are in Paradigms: adjectives and pronouns.
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