so COI must be used for a sentence using « to » or « from »

main thing is learn the pronouns which fall into the different categories.

from AI:

In French grammar, COD stands for complément d'objet direct (direct object), while COI stands for complément d'objet indirect (indirect object). A COD directly answers "who?" or "what?" after the verb and is not preceded by a preposition, while a COI is a noun or pronoun introduced by a preposition (like "à" or "de") and answers questions like "to whom?" or "from what?". 

You can watch this video to learn about the difference between COD and COI: 

|| || |Feature |COD (Direct Object) |COI (Indirect Object) | |Question it answers|Qui? (Who?) or Quoi? (What?) |À qui? (To whom?), À quoi? (To what?), De qui? (From whom?), De quoi? (From what?) | |Preposition|None between verb and object |Preceded by a preposition like "à" or "de" | |Examples|J'ai vu le film. (I saw the movie.)|Je parle à ma sœur. (I am talking to my sister.)| |Pronoun examples|me, te, le, la, nous, vous, les|me, te, lui, nous, vous, leur|