What is the main use of the accusative case?

The accusative case is mainly used for the direct object of verbs. For most of the nouns you will meet, the accusative of masculine and feminine singular will end in with -m and the plural will end in -s. So for example, in the case of 'the boy loves the girl', the girl would be placed in the accusative case as she is the direct object of the verb. In Latin this would translate to, "puer puellam amat". puellam is the accusative of puella.