Use the search bar at the top or google cycling fish tanks. Basically, what you've done is dump fish into a tank that has no bacteria in it. The bacteria is important as it helps break down ammonia (fish wastes) which is poisonous into nitrite. Nitrate is still toxic to fish. The bacteria then break down the nitrite into nitrate, which is much less toxic, and can be tolerated in slightly higher quantities. Ideally, you want to keep all of these levels as close as you can to zero. A nitrite reading of 100ppm is really high. I'm honestly surprised the fish survived. I consider mine way too high if they get to 20ppm.
So, to get this good bacteria into your tank, you need to add a filter and water. The bacteria will already be in the water. Now, they need something to feed on. We know they break down ammonia, so they need a source of ammonia to begin the cycle and start to multiply. You can either cycle a tank without fish or with fish (search fishless cycling, or cycling).
Once the levels of all 3 chemicals are under control (all stable and as close as they can be to 0), then you're ok to begin to add fish slowly. Obviously, you've skipped this step, so now you need a plan to begin to bring the levels under control.
First, water changes are good. They will take out the excess nitrites and ammonia. You should be doing a minimum of 30% every day until the levels are stable. Second, you need to stop cleaning the filter wool. This is where the bacteria live, so every time you clean it, you're killing off heaps of the bacteria, basically starting the cycle from the beginning. You should only need to clean the filter when the flow starts to reduce, and even then, in a tank with no gravel (bacteria can live happily in the gravel too), you should take bits of the filter out at a time to clean, leaving time in between each to allow the bacteria to repopulate.
So, keep up the water changes, and leave the filter alone for a bit. It's good to see you've reduced feeding, believe me, it's pretty hard to stave a fish, so less feeding for now = less pollutants in the water.
Also, I think you've got quite a few goldfish in the tank. They're pretty messy eaters, and create lots of waste. I'm sure that other people with more experience with goldfish will be able to help out here.
I hope that helps, let us know how you get on with the water changes.