Thank you for using the Jiskha Homework Help Forum. True, you don't really have to understand the grammar, the difference between direct-object pronouns and indirect-object pronouns with me, te, nous and vous. If you had a good English class it might be easier. If you are going to have trouble, it will be with the third person.
direct-object pronouns = me (m'), te (t'), le (l'), la (l') and les. Focus on the English for a moment = me, you, him (it), her (it), them.
indirect-object pronouns = lui, leur. Focus again on the English = to, for, at, from (these words MUST be stated or understood) him, her, it, them.
If you have some exercises to do, try those to see if you truly understand the difference. Here are some to study.
Je le comprends = I understand him (or "it" as a masculine singular thing) (direct-object pronoun)
Je lui téléphone = I am phoning him (or "her") (literally = I am placing a phone call TO him/her) (indirect-object pronoun)
Vous devez l'étudiez = You ought to study it (but it could be HIM as well !) = direct-object pronoun.
Vous devez lui écrire = You ought to write TO him. (or to her) The problem comes in English when someones says "You ought to write him/her." BUT they do not mean the word "him/her" so restate it to "You ought to write (a letter/a note/something) TO him/her." Now you are forced to state the word TO, so that is what I mean by stated or understood.
Later you will learn the way to clarify whether lui is to, for, at, from HIM or HER and leur is to, for, at, from THEM (female, male or mixed group)
Please get back with any other questions you have!