In Latin, nouns have cases to tell you what job they are doing in the sentence. There are 6 cases in Latin and each has different endings so you can tell which is which. Here are the basic uses and examples for each case:
Nominative: this is used for the subject of the sentence, or the person/thing doing the action (the BOY runs).
Vocative: this is the case used when someone is being directly addressed ("O, SLAVE").
Accusative: this is used for the object of the sentence, or the person/thing having the action done to them (he hit the SLAVE).
Genitive: this is used to show possession (the BOY'S book).
Dative: this is used for the indirect object and translates into English as "to/for" (he gave the money TO THE SLAVE/he prepared dinner FOR THE MASTER).
Ablative: this has various uses but is often translated "by/with/from" (he was hit BY THE MASTER/he was hit WITH A BALL).