Whoa just means stand there and don’t move until I release you. Using the command while the dog is on birds is part of steadiness training and I believe it’s best to wait until a pup has had a full year hunting wild birds before completing steadiness training. You should prepare yourself to not shoot many birds the first year. For steadiness training I like the method developed by Jeff Funke which is outlined in Chuck Johnson’s book. I like this method because it transitions easily to the field with a neck e-collar for reinforcement rather than a second e-collar on the flank. I’m also fond of this method because I’m now on my third dog bred by Jeff Funke at Three Devils Kennel, she was a started dog and his foundation work easily transfers over to this method.
As far as general training I personally like a lot of the techniques the Smith family uses (Rick and Ronnie) and how they teach dogs without verbal commands. I think their command lead is one of the best dog training tools one can own. It’s amazing how fast a dog learns to heel with that thing being properly used.