Additional to what has already been said. If your fish started to die on the very first day, it has to be resulted from either shock or untreated tap water.
What water conditioner are you using?
If the tap water was untreated, the chlorine can kill the fish fairly fast.
How did you add your fish into your tank?
If you didn't give the fish time to adapt, they can die from the shock rather quickly because the water in the bags you brought them home have different water hardness, PH, and other chemical makeups.
You might also want to read this article to check what mistakes you had make.
Aside shock, the fish has been dying to ammonia poisoning for sure. You did not cycle your tank at all.
