Clicker is just a behavior marker. A click means "you did it right; hold on, a treat is coming". That's it. Nothing more. Nothing less. A verbal "yes!" works the same way as a clicker.

The beauty of clicker training, however, is that it is a consistent marker that you can dole out as quickly or as slowly as the dog performs for you. Once the dog understands what the clicker means, the dog begins offering you behaviors. Thus, you can use the clicker to easily shape new behaviors. The clicker compels the dog to really THINK and problem solve. Once you know how and when to use it, you can use it to teach anything from basic obedience to advanced agility skills to curbing aggression.

Books to read: anything by Karen Pryor.
Links:
http://www.clickersolutions.com/
http://www.clickertraining.com/

Short videos you can buy:
http://www.clickertraining.tv/