Answer:
To keep goldfish healthy, they need clean water so consider a water filter which can be bought from a local aquatic shop and some toys to keep them entertained, some can be attached to a water pump to make bubbles to be fun and entertaining for your fish. Live plants and fake can be bought too to create a real atmosphere. They should be fed every day, for one goldfish they need a pinch of food in the morning and a pinch of food at night but consider more for the more fish you have. You should consider buying some oxygen gravel or just plain to also be more realistic but you could also have sand (from an aquatic shop only!), make sure you don't mix any tropical fish with them unless they are fresh water!