Ok so basically it is a cycle for your fishes safety!
Bacteria are living in your tank I assume breaking down these things, they are called "Nitrifying Bacteria".
First Ammonia, Ammonia is produced from waste such as uneaten food, poop, and decay. This is bad for your fish as this will kill them so you want to get rid of this ASAP if you have fish.
The NB turns Ammonia into Nitrite, Nitrite is also bad for you fish and could kill them. When you see this it is a good sign your cycle is working.
Finally, we have Nitrate which NB turns use Nitrite. Nitrate is good in small amounts like Equal to or less than 40 PPM when you only see this stuff that means your cycle is finished.
Good Parameters look like
Ammonia: 0 PPM / Nitrite: 0 PPM / Nitrate: Less than 40 PPM.
This is needed or else your fish could die from the poisoning of these things!
Ammonia = Nitrite = Nitrate.
Ok, let us go over some basic stuff you might need.
1. De-chlorinator. (Or Seachem)
2. Seachem Prime (Saves your fish from dying)
3. API Freshwater Master Testkit (Must have)
4. Fritz-zyme 700 Turbostart (Makes the cycle go really faster.)
Ok, so I assume your tank is not cycled? We can do the Seachem Prime Fish in Cycle.
First, you should get Seachem Prime and FZ700TS. Seachem Prime will need to be dosed every 48 Hrs and FZ will help you cycle faster.
1. Add FZ700TS
2. Dose Seachem Every 48 hrs until cycled
3. Use your API Freshwater Master Testkit every day to see how your water is doing.
4. Repeat steps 2 and 3 until the reading is Ammonia: 0, Nitrite: 0 and Nitrate: Less than 40
Of course, you need Ammonia to start this but you already got your goldfish so why not use them? Them pooping makes more ammonia so you can use them instead of buying pure like me.
Also while we are at it.
1. Tank Size?
3. What is your pH
4. What are you feeding them?