Summarize the following:
Goldfish, Rosy Barbs, and Guppies are excellent starter fishes. Before you buy your tank and other supplies, determine what kinds of fish and how many fish you will have in the tank. This way, you can buy an appropriate sized tank and the appropriate gravel or substrate. It is recommended that you buy a large tank instead of a small tank. Larger tanks are easier to clean, and you can add more fish to larger tanks. Avoid common myths that tell you it is acceptable to keep fish in bowls. Larger tanks also allow your fish to grow while still being comfortable. Keeping fish in an overcrowded tank is the fastest way to reduce water quality and introduce toxins and diseases to the water.  It is recommended that you start with a fish tank that can hold between 20 and 55 gallons. For smaller fish, use a tank that can hold around 10 gallons. It is also better to buy a wide tank instead of a tall tank. Wide tanks have more surface area, and thus, allow more oxygen to enter the water and more waste gasses to escape. Gravel, or substrate, comes in various sizes, colors, and forms. You can choose from gravel, sand, or crushed coral. Gravel is the most common form of substrate and comes in small to large sizes. It is recommended that you buy gravel that is medium in size.  Do not buy gravel with sharp edges. The sharp edges can harm the fish's scales. Fish that like to pick up the gravel or dig into the gravel are especially at risk. Sand substrate is great for fish with delicate barbells, such as the Corydoras catfish. However, it is very difficult to clean and can get stuck in your filter. If you have a picky eater, like a puffer fish, it might swallow the substrate. Crushed coral gravel is great for fish that prefer a higher pH, such as African cichlids, as this reflects on their natural habitat. There are three different types of filtration systems: external, internal, and under gravel. However, whichever you choose, make sure it is high-quality. Internal filters are great for small tanks.  Under gravel filters move the water through the gravel, which induces biological filtration to occur. They pull water in and they release it out of the spout. Examples of high-quality filters are the Fluval External filter, Penn Plax Cascade canister, and the EHEIM Classic External canister. There are a variety of decorations you can choose from. There are aquarium backdrops, rocks, driftwood, plants (both real and fake), and furniture or decoration caves, tunnels, and bridges. Make sure to purchase a variety of decorations. A starter kit tank though comes with a rather childish decor, as it is marketed toward children.  Plants and furniture allow your fish to hide out, feel safe, and relieve stress. However, for more greedy, herbivorous fish, make sure to get more sturdy, nip-proof plants. Aquarium backdrops are great for hiding cables and equipment behind the tank. They also create an illusion of depth for the fish. Make sure the decorations you buy are safe and non-toxic sharp objects are harmful to fish, especially to the Eye goldfish and the Black Moor fish.

Summary:
Determine what kind of fish you want. Buy a tank. Select the appropriate gravel. Choose a high-quality filter. Pick your decorations.