Quality flower suppliers should always attach a complimentary packet of flower food. Read the packet for saturation quantities. You may be able to use half the packet and save the second half when you change the water when it begins to look a little cloudy.
Cut carefully the rubber band attaching the packet to the stems. You don't want to damage the stems.
Pour into a clean vase filled with clear water.
It may look slightly cloudy before mixing throughly.
Use a non-metallic spoon to thoroughly stir the mixture into the vase.
I like Crystal Clear because it is quickly soluble and the vase is ready to grid.