1. Don't put the fish outside, there inside pets. If you want outside fish try goldfish or koi.
2. Don't put boiling water in the fish tank, drain out 1/4 of the water and replace it with water that feels mildly warm on the underside of your wrist like you would a babys water. A human thermometer will work BUT a aquarium thermometer with a suction cup is extremly cheap and useful to keep an eye on your tank. Either that or turn up the heater a hair, be careful not to turn up the temp too fast or you will do more harm than good.
3. Aquarium salt is what you want, it will be also rather cheap and is a good thing to keep on hand. Any place that sells a pet fish should have this.
You do have a heater right? Take the temp of the water, it needs to be around 25-28 celcius.
It might be overall too late but the best results may be just to get rid of about 90% of the fish asap. Unless you make some serious changes you will be dealing with this again shortly.