Summarize this article in one sentence.
You will need specific equipment and tank dimensions to properly house your goldfish.  By providing the right environment for your goldfish, you will help your new friend to be comfortable and healthy in its new home.  For the aquarium itself, you should try to find one that is around 20 gallons (76 L) in size.  This may seem large for your new fish, but remember, it will grow over time. Bowls, contrary to popular belief, are potentially lethal to goldfish. You will need both a water filter and an air pump.  Sometimes these are combined into one device.  You will also need to buy filters for the water filter itself. Additional items will include a stand and cover for the tank.  These help keep the fish safe and secure in its new home. Make sure you find a compatible UV light for the tank. This is important because not all reptile UV units are safe to use near water. Some filters or covers come with a light built in. However, if your cover doesn't include a light you will need to add a separate one.  Run the light for 12 hours a day. Inside the tank you will want to place both sand, along the bottom, and then decorations to sit on the sand. Gravel and larger rocks can be dangerous as goldfish may accidentally swallow them and possibly perish. Also, the larger gaps between pieces of gravel trap poop which is quite unsanitary for your new pet. Finally, you will want to purchase fish food.  These are found in pet stores and usually come in the form of flakes. Before you start assembling your aquarium, you will need to take a few steps to make sure it is a safe and healthy place for your new fish.  Make sure you do the following before adding any water or your fish:  Wash and rinse the tank, decorations, and gravel to make sure they are clean.  Don't use any soap or detergents. Put the aquarium in a safe and stable place in your home. Once you fill the tank with water, it will be very heavy. So make sure to select a location where you'd like to house the tank long-term. The surface you set the tank on should also be stable and strong enough to hold the tank when full of water. After you have cleaned the tank and the items that will go into it, you can start putting them into the tank.  Have fun decorating the tank and setting it up to be a great and safe place for your fish to live.  Place the gravel first, covering the bottom of the tank. Add your decorations next.  Have fun making the tank look interesting to you. After you have cleaned and arranged the tank to your liking, it's time to add the water.  Pour the water in slowly to avoid disrupting your arrangement or stirring up the gravel at the bottom of the tank.  The water should be room temperature, around 65° to 75°F. Add a dechlorinator to the water to remove harmful chlorine from the water. Once the tank is full with clean, room temperature water, you can add your filter and air pump.  Some filters may also function as an air pump, in which case you will not need both.  Your filter will help keep the water clean and free of waste produced by your fish. Air pumps, and some filters, will add oxygen to the fish's water, which it needs to breathe. Turn on the filters, air pumps and lights to make sure everything in the tank is running properly.  Leave the filters and air pumps on to prepare the water before adding your fish.  Keep an eye on the temperature to make sure it remains between 65° to 75°F. If you drop your fish into the new tank water without letting it acclimate, the fish may become shocked and die.  There are differences in the quality of the water that your fish will be sensitive to.  Give the fish time to acclimate properly before adding it to the tank.  Add 2 cups of tank water to the bag that your fish is in. Add another 2 cups of tank water to the fish's bag every five minutes. Stop when you have added 8 cups of tank water to your fish's bag. If you want to (and can), you can use drip acclimation for about 30 minutes to an hour. Carefully net your fish and add it to the tank.  Dumping the fish and bag water into the tank can also dump any waste the fish may have released.

Summary:
Purchase the proper items to house your fish. Prepare the aquarium. Add the gravel and decorations to the aquarium. Pour in the water. Add your filter and air pumps to the tank. Test the tank. Introduce your fish to new water slowly.