Direct object pronouns replace nouns that 'receive the action of the verb' if those nouns are not preceded by a preposition:

Mon petit frère réveille mes parents à trois heures du matin.
(My baby brother wakes my parents up at 3 o' clock in the morning.)

Mon petit frère les réveille à cinq heures et demie aussi.
(My baby brother wakes them up at five thirty as well.)

Here are the direct object pronouns:

Person
Singular
Plural
1st
me (m')
nous
2nd
te (t')
vous
3rd
le (l')
les
la (l')

Examples:

Il regardait la mer pendant des heures, il la regardait avec attention comme si il la voyait pour la première fois.

Mon petit frère achète toujours beaucoup de livres; il les achète d'occasion et les prête à ses amis quand il a fini de les lire.

Things to remember:

Direct object pronouns go just before the verb of which they are the direct object. This gets tricky with negatives and compound tenses. More on placement.

Example:

Mes voisins, je ne les vois pas tous les jours mais quand nous nous voyons nous aimons parler ensemble.

Mon voisin, je l' ai vu la semaine dernière devant l'immeuble. Mon professeur d'histoire, je l' ai rencontré dans la rue l'autre jour.

 

Things to be careful about:

1)
'Nous' and 'vous' look the same here as the equivalent subject pronouns, indirect object pronouns, and reflexive pronouns. You have to keep an open mind when you come across these words in your reading and consider all possibilities.

 

2)
'Me' and 'te' (and 'm'' and 't'') are the same as the equivalent indirect object pronouns and reflexive pronouns. It is easy to fall into the trap of thinking a sentence like the following is reflexive:

Maman me réveille à sept heures du matin.
(Mom wakes me up at seven in the morning.)


But you can tell it is not a reflexive sentence because the subject ('Maman') is not the same as the pronoun ('me'). The following would be reflexive:

-)  Maman se réveille à six heures et demie.
(Mom wakes up at six thirty.)

(Maman = se)

-)  Je me réveille à onze heures le week-end.
(I wake up at eleven on the weekend.)

(Je = me)


3)
'le', 'la' (and 'l'') and 'les' look exactly like definite articles ('the'). Out of context, it is impossible to tell the difference (there are the same masculine/feminine, singular/plural forms, plus the apostrophied form before a vowel or mute 'h'.

You can tell the difference from the context, though:
          - articles go before nouns (sometimes before adjectives first)
          - pronouns go before verbs (sometimes there are other pronouns first)

Mon frère les réveille. ('réveille' is clearly a verb)
Je la mange. ('mange' is clearly a verb)

Il la ferme.
(true, 'la ferme' could mean 'the farm', but the rest of the context wouldn't make sense: it has to mean 'he closes it')