The accusative case, in English, is better called the objective case. It identifies the object, the thing that the subject is directly acting on.

Example: the boy breaks the chair.

Boy is doing the action, he is the subject, and NOMINATIVE.

The chair is being acted on, it is the object of the action, and so is in the OBJECTIVE, or ACCUSATIVE case.

Imagine a hand floating right after the verb, with a finger pointing at the object the verb is referring to. The finger pointing at the chair is ‘accusing’ the chair. The boy breaks. Finger pointing forward, ‘what does he break?’ – he breaks the chair.

I would suggest you spend some time listening to the “My First Latin Lessons” on the latinum podcast, where these matters are clearly explained.

http://latinum.mypodcast.com