les pronoms objets directs

A direct object is a noun following  the verb that  answers the questions 'what?' or 'whom?' Remember  a pronoun replaces a noun, and in this case the noun is a direct object. For example, Superman might ask: 'Lois, will you call me tonight?',  where the direct object pronoun 'me' stands for Superman. 

Whether a verb takes a direct object or not depends on whether the specific verb is transitive or intransitive.

forms and uses

In front of a word starting with a vowel, le and la become l'; me becomes m'; te becomes t'.

Direct object pronouns in French agree in number and gender with the nouns they replace.

Note that le/l' can replace an adjective or a verb.

placement

Direct object pronouns precede the verb of which they are the object. In a composed tense (like the passé composé), the pronoun precedes the auxiliary. In infinitive constructions, the pronoun goes immediately before the infinitive. When the conjugated verb is negative, the ne comes before the object pronoun. 

In the negative imperative, the pronoun follows the normal placement before the verb. However, in the affirmative imperative, the object pronoun goes after the verb and is attached to it by a hyphen. In addition, me and te become moi and toi.

agreement of the past participle

The past participle agrees in gender and in number with a preceding direct object. In other words, if the direct object pronoun is feminine, add an e to the end of the past participle; if the pronoun is masculine plural, add an s (unless the past participle already ends in s); if it is feminine plural, add es.