Nominative is the case of subject’s personal verb forms, and therefore of everything concerning the subject. Caesar venit. Puer est laetus. Hannibal prīmus in proelium ībat.
ITt serves to ‘name’ (nōmināre), the nominative is used in conjunction with de + ablative, for book titles:
Bellum civīle. Coniūrātiō Catilinae.
From this value derives also the exclamation nominative, alternating with the accusative form: Fabulae!, Nugae!
Vocative
The vocative is the case of the person questioned: it is used to call the attention of another person. We must remember that, except nouns of the second declension finished in -us, the vocative is always like the nominative.
Conficior enim maerōre, mea Terentia.
Salvē, alumnule.
Accusative
The accusative case is used to designate the primary purpose or the result of the verbal action. From this general sense are deducted particular uses of the accusative, which will be summarized in the following lines:
Direct object:
The accusative case is used to express the direct object of transitive verbs (or used transitively).
Brutus epistulam ad amīcum mīsit. Militēs pontem fecērunt.
Direction accusative:
The accusative of direction indicates the destination of the verbal action, responding to the question quo. This add-on is constructed in the accusative with or without preposition:
Without a preposition: with names of cities and islands, with nouns as domus, humus and rus.
Eō Rōmam.
With the prepositions in, ad in other cases.
Legātus in Hispaniam missus est.
Militēs ad oppidum appropinquant.
The preposition “in” indicates movement into a place, while “ad” indicates movement to the surroundings, hence, in contexts of hostility.
Peditēs tela in hostium equitātum iaciunt.
The preposition ad with ac:cusative can appear with verbs that do not express movement, responding to the question ubi (‘place where’):
Ad exercitum manēre.
Exclamation accusative:
In exclamations, and in concurrence with the nominative, Latin uses the accusative.
Mē miserum!
This exclamatory accusative may be accompanied by interjections and, in few occasion, by the enclitic particle-ne:
