Cycling is the process of starting the nitrogen cycle. Because the process involves developing bacterial colonies, capable of converting highly toxic waste material to forms that can be used by plants or be purified, it takes time. Unless your fish is a hardy breed, they will not survive the process because they cannot handle the high levels of toxins. If you’re not familiar with the nitrogen cycle, you may want to read the article first before reading this one. This article will make a lot more sense if you do. One of the first things you’ll want to do is get a nitrogen test kit. They’re inexpensive and widely available at most pet or fish stores. With the kit, you’re going to check for the presence of ammonia, the nitrite, and finally nitrate. Once the nitrogen cycle is established, you should not see any ammonia or nitrites. 
If you see ammonia but no nitrites, you’ll know the bacteria that converts ammonia to nitrites are still colonizing your aquarium. If you see nitrites but no nitrates, you’ll know the bacteria that converts nitrites to nitrates haven’t developed. By the time you’re ready to cycle your aquarium tank, you should have your substrate in place. You probably don’t want to use a full tank. It takes longer to cycle and while you’re doing this, you may want to make changes. Using a 1/3 or 1/2 filled tank is optimal. Before cycling your tank, make sure your water quality is where you want it. A lot of cities add chemicals to the water supply so check the pH and the presence of copper (copper is deadly to invertebrates).
Natural Way
If you don’t have access to an established aquarium, you can put a few flakes of fish food every 12 hours. Once the food starts to decompose, it’ll release ammonia, which will attract your first class of bacteria. Once they convert the ammonia to nitrites, it’ll attract th second class of bacteria. Instead of fish food, you can drop in a small chunk of raw fish or shrimp. Use a 1 inch by 2 inch piece. Alternatively, you can use ammonia. Ammonia is commonly sold near the cleaning supplies in grocery stores. Make sure it’s pure ammonia and doesn’t have any additives like perfume or soap. Add about 5 drops per 10 gallon every day or until ammonia registers on your nitrogen test kit. Once you see detect nitrite, cut the dosage in half and continue until you detect nitrates. This entire process can take a week or two. Be patient.
Jumpstarting The Process
The quickest and cheapest method is to use an aquarium that’s already been established to introduce the necessary bacteria to your aquarium. All you really need is a small scoop of their substrate to introduce the necessary bacteria. These bacteria live in both freshwater and saltwater so it doesn’t matter what type of aquarium they come from. You can get a small sample from a friend who has their own aquarium or even your local pet store or fish shop (if you ask nicely). Actually, the filter material is a better source of the bacteria but the substrate is easier to obtain. Make sure the nitrogen cycle has been firmly established by feeding your aquarium fish flakes until you regularly detect nitrates.
Nitrogen Cycle Kits
There are a number of products that contain the necessary bacteria to seed your tank. Some even claim to do it in 24 hours but they’re also quite expensive. If you don’t want to wait and money is not a concern, use the nitrogen cycle kits.
Final Step
Although nitrates are far less toxic than nitrites or ammonia, it’s still toxic. Before adding fish, perform a 30% water change to reduce the nitrates. And your aquarium is fully cycled.