Using a baseball analogy is an effective way to begin to teach hand signals. It’s best to have some visual aid at each base; like the flags or white buckets.
You can start playing baseball in a small area like your back yard and eventually go to a field when it‘s time to extend the distances and even drop the flags. When you get to that stage, you can begin to hide birds in the three base positions as long as when you start hiding you shorten the distance once again because you always want to teach to a successful result. Before you get to the point where you are playing baseball at say 50 yard distances, you should teach your dog to sit on the whistle. As you extend distance, you give the dog more opportunity to veer off line and the whistle helps stop and redirect him.