Right.
Your fish produce ammonia. Ammonia is poisonous, seriously poisonous, to fish. When your filter is cycled, it has some bacteria in it which converts the ammonia into something called nitrite. Unfortunately, nitrite is also poisonous, seriously poisonoius to fish. When your filter is cycled, it has some bacteria in it which converts the nitrite into nitrate. Fortunately, nitrate isn't particularly poisonous.
Until you've grown your bacteria (ie cycled your filter), you need to remove the ammonia and nitrite from the water yourself. This stops the water being poisonous, seriously poisonous.
You have to get some jugs or buckets or whatever, and take water out of your tank. About 90% of it. By this I mean nearly all of it. Not just halfway. Then you get some fresh water from your tap (by this I mean "faucet" if that's what you call the things that give you water), add the correct dose of that Tetra Start stuff that you bought on November 14th, make sure it's roughly the same temperature as the water that you took out, and put this fresh water back into your tank.
Before the water comes out of your tap (by this I mean "faucet"), generally it gets treated with either chlorine or chloramine. They do this because the chlorine or chloramine kills the bacteria which could make you sick, so it means you can drink the water. Because it kills bacteria, it will kill the bacteria in your filter, if you don't use that Tetra Start stuff. So whenever you need to put water near the tank, you should always use that Tetra Start stuff, to make sure you don't kill the bacteria in the filter.
You clearly haven't bothered to buy a test kit, so you'll have to be bothered to do this process every day. Not just when you fancy it. Every day. Unless you want to keep having fish die.
The problem with not having a test kit is that you don't know when the bacteria have grown sufficiently in your filter. So you have two choices. 1) You can do the above process every day for 6 months or 2) You can buy a test kit. It needs to be a LIQUID based kit as the paper strips things are not very good. If you do choose to buy a test kit, let us know, and we can let you know how to modify the above process so that it's not quite such hard work.
Now, all the above only counts if you have at least one fish in your tank. Remember that in order to grow the bacteria, they need to be fed ammonia, and that comes from a fish.
You need to understand the processes that are going on in your tank to avoid making further mistakes and killing more fish.