Quick Start should be added to dechlorinated water, otherwise the chlorine can harm the beneficial bacteria it contains, as well as the fish you are trying to keep. It is recommended to treat the water first with API Tap Water Conditioner before adding new water to the tank, to remove the chlorine and chloramines. The Quick Start would then be added directly to the aquarium. Quick Start contains only the live bacteria -- it does not contain a dechlorinator, so both are necessary for a happy and healthy aquarium.
It's recommended when removing chlorine and detoxify heavy metals to add: 1 mL for each 20 U.S. gallons (76 L) of aquarium water. To detoxify chloramines: add 5 mL for each 30 U.S. gallons (114 L) of aquarium water.