You need...
Food. Usually, people start with commercial feed – chick starter for ducklings and layer feed for adults. Some people branch out into natural feeds later on. Many people feed their ducks veggies and fruits such as tomatoes, lettuce, cabbage, cucumbers, apples, and more. Many people also feed mealworms. I feed my ducks wheat and sorghum, as well. You also need a feeder for the commercial feed or grain. You can either offer the food free-choice (24/7) or at scheduled times. I offer it twice a day, morning and evening.
Water. You need a waterer, and the water needs to be refilled every day, sometimes twice a day. It needs to be scrubbed clean of algae every few weeks. Once they have feathers, you can give them a bathtub. The waterer needs to be deep enough that they can submerge their entire bill.
Shelter. It should be predator-proof. It doesn't need to be large for just two ducks, maybe 3x3 feet is enough. It needs to be cleaned regularly. It should have a nest.
A pen. Again, doesn't need to be large, but bigger than the shelter so they have room to forage. It needs a fence and some shade.
Care. Every day, you need to feed them, give them water, clean their pen (maybe every couple days), and then spend time with them so they will be tame. Don't chase them any more than necessary. Get them used to your presence by just sitting nearby and reading. You can progress to giving them treats out of your hands once they are comfortable near you.
(Oops, just now noticed, much of this information is a duplicate of Jon's.)
