can anyone explain difference betwixt accusative and nominative for german?
In shortest, nominative is used for subject of the sentence, and accusative for object.
Consider the sentence "The dog bites the man". In German this is "Der Hund beißt den Mann". "Der" in front of "Hund" indicates nominative ("dog" is subject) and "den" in front of "Mann" indicates accusative (because "man" is object in this sentence).
Notice that english language lacks this distinction, because it doesn't have accusative. In English, we know who bites whom only because of sentence structure.
In German, however, we know who bites whom because of used cases. That is why is in German language possible to replace positions of object and subject in sentence (verb still must be on second place though) so you can say "Den Mann beißt der Hund" - there we have "man" on first place, but still accusative, and "dog" on last place, and still nominative, so the sentence has still exactly the same meaning "The dog bites the man", and not "The man bites the dog", as some English speakers could suspect.
This position reversal in German language is, while correct, somewhat rare in practice (at least that is my experience).
To start you off, quite a lot of sentences have something doing something via a verb. (the dog eats the bone etc) The thing doing the action is the subject and that goes in the nominative. the thing being done to is the direct object and that goes in the accusative. These things get called other names by some people. So in my sentence, the dog is the subject and the bone is the object. so the dog is in the nominative case and the bone is in the accusative case....
Nominativ does not mean its the subject, but the regular subject needs to be Nominativ. Akkusativ also does not mean its an object, but in most cases the direct object is an Akkusativ (which case is needed, depends on the verb).
Both Nominativ and Akkusativ do more things than just being subject and being an object.
The terms subject & object, Nominativ & Akkusativ are not interchangable. They describe different things (which are connected with each other, but they are not the same).
If you translate from english to german. You take the english subject and make it the subject of your german sentence (and thats most likely just a Nominativ or some Nominativ + Genitiv Kombination). You take the entire predicate and make an equal predicate in your german sentence. You take the english object and create a german object in the Kasus that is fitting the verb of the predicate (and that might very likely be Akkusativ, but it could be also something else).