The accusative case, akkusativ, is the one that is used to convey the direct object of a sentence; the person or thing being affected by the action carried out by the subject. This is achieved in different ways in different languages.
Step 1: Word order
Word order is not as important in German as it is in English.
"The dog loves the cat" has a different meaning as "The cat loves the dog". In German, we can switch places and the dog will still be the one loving the cat!
Der Hund liebt die Katze. = Die Katze liebt der Hund.
The dog is the agent or subject, the one loving.
Wait, so how can I say “the cat loves the dog”?
In this case you would say:
Die Katze liebt denHund.
This change from der Hund to den Hund is what we call "declension". To be precise this is the "accusative declension".
Step 2: Understanding functions
A sentence is like a factory, where every worker (every part of the sentence) has a role to play, a job to do.
Sounds interesting, tell me more!
The function of "dog" can change. If we say der Hund, we mean the dog is the agent or subject, if we say den Hund we know it is the direct object. Someone else is loving it.
So the job of "dog" is either to be the subject or the object of the sentence. To mark what kind of job the dog is doing, we use declensions.
And in English we express the functions by means of word order, while in German by means of declensions.
You are a genius!
Step 3: Understanding "cases"
I have heard something about "cases", what does that mean?
Let me show you a little table...
Who is performing the action?
Who or what was something done to?
Do I really need to know all of this to be able to speak German?
To be honest, you don't. Many students get frustrated with declensions and cases and accusative and nominative, but it is actually not essential to be fluent. In fact, it is more important you spend time learning words and practicing verbs, than mastering declensions!
Okay, but I still want to know how this story ends.
Mann as a subject → Nominative
Der Mann spricht Französisch.
Mann as a direct object → Accusative
Ich seheden Mann.
All the other articles remain the same in accusative!
We have two more cases in German, but if you understood this, you understood 80% of the declensions delights.