Different dumplings match with a different kind of gravy. Russian or meat dumplings should be served with sliced onion fried until light brown on a pan with hot butter of margarine. You can also add some sliced mushrooms to the pan with onions and margarine. These dumplings are also delicious when served with Spaghetti sauces (for instance Hunt's).
Russian dumplings can be not only cooked but also fried or baked inside the oven. You can also fry them in a pan with butter or margarine after cooking first until their edges would be light brown. You can also bake it in hot oven (450o C) for 30-45 minutes and then serve them for instance with a clear beef soup.
Dumplings with blueberries or any other fruit are the best with the sauce made of cream mixed with some sugar and vanilla and cooled. These dumplings are usually served during summer because of the availability of fresh fruit and also the way how they are prepared (with cool sauce).
Finally let me tell you about "Christmas" dumplings, that means the mushrooms or cabbage dumplings. For Christmas we eat these dumplings with borscht (red beets soup) or mushroom soup for cabbage dumplings. Cabbage dumplings are not only served during Christmas, they may be also served through the whole year, but dry mushroom dumplings (especially so called "uszka") are usually done just once a year on Christmas Eve.
Cabbage dumplings are also delicious with the same gravy as used for Russian dumplings.
Now, I wish you good luck with dumplings' preparation!
If you are interested in Polish cuisine I recommend to you a book written by Marja Ochorowicz-Monatowa, entitled Polish Cookery