The nominative indicates the subject or the predicate complement of the sentence. The singular form does not have a suffix. The plural suffix is -t.
The genitive indicates the possessor. It often corresponds to the English genitive suffix 's or the preposition of. The genitive suffix is -n in the singular and -en/-in/-den/-tten/-ten in the plural. The plural suffix which is selected depends on the type of word, but there are often many alternatives, anyway.
The accusative indicates the object of the action. In the singular, the accusative has either no suffix or its suffix is -n/-t. Thus all the nominals, except for some exceptions, have two accusative forms which are always similar either to the nominative or the genitive. The accusative suffix which is selected depends on the context in the sentence. The accusative singular suffix -t is used only with personal pronouns and the interrogative pronoun kuka 'who'. In the plural, the accusative suffix is always -t and that makes the form similar to the nominative plural.