What is clicker training?
A lot of dog trainers and their students will use a dog clicker (a small object that makes a click sound) to help train and condition their dog.
The advantage with using a dog clicker is it makes for a clear marker (a word or sound used to indicate to a dog that something they're doing is desired) of a wanted behaviour right before giving them a reward for that action.
Using a clicker allows you to not have to rely on your dog either being able to hear your verbal cue and its tone because it always makes the same consistent sound, that helps provide more consistent training and conditioning.
The disadvantage with a clicker is that if ever you don't have it with you and you've become fully reliant on it then you will want to make sure you practice with multiple markers like saying "Yes!" by then, and not just the clicker.