Place the sluice in the flow of a stream or river so that the water enters the flared end and flows through the sluice. If the current is strong you may need to lay some stones against the edge of the sluice to keep it from washing away.
The sluice should be set at a downhill angle that allows the material to briskly flow through the sluice. The higher the volume of water available the shallower the angle will be. The important factor is that the material you shovel into the sluice will flow through the sluice. Sometimes you will find that it helps to classify the material before you put it into the sluice by passing the material through a screen. Pre-classified material will run through the sluice at a more uniform rate.
Shovel material into the sluice at the flared end as close to the end as possible so that the material is washed over the entire length of the sluice.
Do not overload the sluice with material. Pace your shoveling so that the sluice has time to clear before you add more material.
When you are ready to clean out the concentrates remove the sluice from the water and tip it down into a bucket or tub. Wash as much material as possible out of the sluice into the tub and then remove the riffle tray and carpet and wash both of them out into the tub. Replace the carpet and riffle tray into the sluice and you are ready to go again. The concentrates of heavier material and gold are now in the tub so that you can remove the gold from the concentrates with a gold pan or some other clean up tool.