I personally have never made it. But a google search on “rolladen recipe” has yeilded three pages of results. Rather than point you to a specific recipe, I suggest you google it and pick whatever recipe suits you best.
You get the Rouladen (beef for preference as meat) and cover the side you are going to roll up with a slim layer of mustard, use salt and pepper (its a bit of experience) and fill it with thin chopped onions pickles and bacon and roll them up, fasten with toothpicks so the filling cant quell out.
Fry them short and hot directly in the pot you are going to use to cook them then add the water. For the sauce I usually use a premade sauce, I am not that much of a cook as bachelor, my mother could maybe tell you more, unfortunally she is neither online nor speals any english, but most brown sauces will actually do, I think she (mommy) uses beef bouillon soup to make the sauce. Cook them for at least an hour and a half, the meat should be tender enough to cut it with a spoon. keep the lid on the pot while cooking the rouladen need to be covered with the sauce all time.
Serve sidedishes as you want, I advise to mashed potatoes and some steamed vegetables like peas and carrots.