I use a product called Wardley's Chlor Out. It removes both chlorine and chloramines which are sometimes used to purify the public water supply, but which will harm the fish.
It is inexpensive, compared to many of the other products, and works well.
Brenden, i use Tetra AquaSafe(bright yellow bottle), it's found in most walmart stores. It will neutralize chlorine, chloramine, ammonia, and various other chemicals. It costs a little more than other brands, but it seems to be worth it. I have never had a problem with it and in my research on fish info I have seen it recommended by various websites. But go with your instincts(and price range) and hopefully everything works out .
If you mean HOW to do it, I usually use a 2 gallon pot to mix my water in. I first put the dechlorinator drops in using the directions on the bottle. (They vary according to brand) Then I run hot and cold water in until it reaches the correct temperature for my tank (using a thermometer). Then I just pour it into the tank to replace what I have taken out.