This type of a practice generally moves from one pose to another on every breath. As an example – inhale lift the arms overhead, exhale fold forward….or inhale step back to plank pose, exhale lower down in chattaranga (or knees chest chin to the floor), inhale to cobra, exhale to downward facing dog.
In some flow classes things might start off a little slower taking a couple of breaths in each pose, and then gain speed by moving on every breath. This is a very common style of class and can get your heart rate up a bit, while building strength and balance and working your core. The ongoing movements make it extremely important to focus on your breath as a source of energy for the movements, otherwise if you end up holding your breath the whole practice gets harder – and yes, I do know this from experience.