A noun in Latin can have six basic attitudes, each of which tells you something about how the word is being used. We call these attitudes the “cases”. Let’s take passer as an example. Passer is a sparrow. The common house sparrow is called passer domesticus.
Here are six cases of the noun passer.
passer – sparrow (nominative)
passer – sparrow (vocative)
passerem – sparrow (accusative)
passeris – sparrow (genitive)
passeri – sparrow (dative)
passere – sparrow (ablative)
The first four of these cases are simple to grasp in their basic meanings. We will extend these explanations into more detail as we progress, but getting the basics right is most of the battle.