What is the difference between the COI and COD in French?

Called "COD" (Direct Object Pronoun) and "COI" (Indirect Object Pronoun) in French, there are not used in the same context as in English. 

For example: Je connais Jean. -> Je connais QUI? = Jean. QUI = WHO means it is a Direct Pronoun. 

However, Elle parle de Jessica. --> Elle parle DE QUI? = Jessica. Jessica is the indirect object of the verb "parler". 

And like in English, it is possible to substitute the object with pronouns. 

Je connais Jean --> Je le connais. = I know him. The COD in this case is Jean that can be replaced by "him". The list of the pronouns are: me, te, le/la, nous, vous, les". 

Elle parle de Jessica --> Elle parle d'elle = She talks about her. The COI in this case is Jessica that can be replaced by "elle". The list of the pronouns in this case are: "me, te, lui/elle, nous, vous, leur".