How does the retriever know what you expect from him?

If you want to use a word as an order it has to be short and not a long sentence. Instead of: "Sammy, now sit with me and behave!" Say: "Sammy, sit!" Every action needs its own order. Don't use "Shoo!" for different actions. What is it your dog has to do now? Get out of the way, lie down, or go to his place next to the chimney?

Calling your dog with a whistle has to be different than calling him with your hand. Your dog needs the opportunity to understand your order. Therefore, for his training choose a calm place with few distractions where you can totally concentrate on your puppy. The most convenient thing would be to give him the order when he is about to do the desired action. For your dog to relate the action with the order the most important thing is exact "timing".

For example if you want to teach your dog the order "Sit!" You could wait until he is about to sit, then at the same time you say "Sit!" When he has seated, he receives a prize. This is the ideal way to teach your dog something, but it means you'll have to be paying a lot of attention, so as to give the order coincidentally the same time as the action. During active training you can help your dog by stimulating him to do a determined action on. To learn the order "Sit!", hold and at double prize in front of his nose until he notices it, then slightly move your hand up and down. In that moment you will give the order to "Sit!" and your dog will receive the prize.