Direct objects receive the action of the verb, or as we say more simply, it’s the noun in the sentence that is being verbed. So, in “Candidus reads the letter,” the letter is the direct object.
In Latin, the direct object is always in the accusative case. See if your 3rd grader can recite all the declension chants! The accusative row is the 4th one down. Those are the endings to look for to spot direct objects in Latin sentences.
Click here for the 1st declension chant audio file.
Click here for the 2nd declension (masculine) chant audio file.
Click here for the 2nd declension (neuter) chant audio file.