I saw somewhere that it is better to keep water out for a while before actually using it for fish.
1.Why is this?
2.How long should you leave the water standing?
3.I filled up a large bucket with tap water and put saran wrap over the top and put it on my floor. Is this how you do it?
4.Does this REALLY help/make a difference?

Thanks!

Water is supposed to be out for at least 24 hours for three main reasons, 1 is chlorine evaporation. Chlorine can obviously kill your fish and will evaporate out of the water in about 24 hrs. 2 is for stablizing temperature. you want to add water that is the same temp of your betta tank. if you aren't using a heater, then you want to have that aged water be room temperature (the same as your betta tank) if you are using a heater you need to heat the water up before you add it so that it's matched with your heated tank. if you run cold water out of the tank, you need to let it stand to become warmer etc. etc. 3 is for the diffusion of the air bubbles that tap water has. i'm am not familiar with the exact term, but the air bubbles you see when you use water straight from the tap can rest on the body of your fish and actually harm a betta's gills. if you leave the water out for 24 hrs these air bubbles will pop and you won't have problems with that.

Don't put saran wrap over the top of the container when you are leaving the water out to set because it actually needs that open air to evaporate and let the chlorine escape.

Yes, leaving your water out to stand for 24 hrs. REALLY does help and definately makes a difference to your fish!

actually keeping water over night will do.. 24 hours is to be 100% sure.. but each country and each region has different water content where different water is treated with different amount of chemical..

but do take note, chlorine does evaporate, but not chloramine.. u need a chloramine remover to do the job..

secondly, if you leave water overnight for tooooo long, say 48 hours.. this will bring the PH down.. this is due to chemical reaction that introduce a bit of acid.. and the oxygen level goes down too...

best way to store water overnight or even long period of time, is to use an air pump and air stone... and have some water plants floating on top..

yes, but if you have an airstone in the tank, why would you need to add the airstone to the water sitting out?