To pan for gold you first need to place some gold-bearing materials, such as river gravel, into a shallow pan, then add some water, and finally carefully swirl the mixture around so the water and light material spilled over the side.
To use a rocker, you first had to dump dirt and rock on the top, followed by a bucket of water. The cradle was then rocked by hand to stir the mixture. The big rocks were caught in the sieve, the waste exited the lower end with the water, and the heavy gold fell to the bottom of the box and was caught on the riffles.
To use a sluice box, rivers would have to be diverted into ditches. Then you could soften the gold-bearing dirt and rock. After that, the miners would loosen the dirt and rocks with picks and allow water and gravity to transport the material down to a sluice box.