Pronouns are used to refer to people and things that have already been mentioned. The main pronouns you need to be familiar with are:
a) subject pronouns (like je, tu, il, etc.)
b) direct object pronouns (like le, les, me, te)
c) indirect object pronouns (like lui, leur, me, te)
d) relative pronouns (like qui, que, dont)
e) possessive pronouns (like le mien, la tienne)
f) locative pronoun y
g) partitive pronoun en
h) independent pronouns (like moi and toi)
In order to successfully write with pronouns, you need to familiarize yourself with the different forms, the contexts in which they are used, and the order in which they appear.