Why is it "ein Fischsandwich"? Shouldn't an accusative case (einen) be used in this sentence, as the action of eating is being done on the fish sandwich?
It's "das Sandwich". In the accusative case der --> einen, die --> eine, das--> ein.
Actually, Sandwich can be both masculine or neuter. In the neuter case it's as mainecoon told you. In the masculine case: 'Ich esse einen Sandwich' Depending on where you are in Germany, the masculine or the neuter form is more common. http://www.duden.de/rechtschreibung/Sandwich
If you want to hyphenate the word, the correct spelling is "Fisch-Sandwich" since you connect two nouns. In German, usage of the hyphen is rather free and to some part a matter of taste and style. If it connects two nouns, it is mainly used to 1) emphasize a component of the word 2) to disambiguate between different interpretations of the word 3) to make long combinations of words more readable. You can find some examples here: http://www.duden.de/sprachwissen/rechtschreibregeln/bindestrich#K21 As a rule of thumb: don't use it unless you have a special reason to do so. In the case of 'Fischsandwich' I wouldn't use it.
hey do you think you could also explain the seeing ones in german to i do not get those at all there is so many and they all mean the same dang thang