Deep slow breaths in
Incentive spirometers aid in opening up the passages and air sacs of the lungs, especially after surgery that requires a ventilator. The device is simple but the technique is key: fully exhale and then slowly inhale through the tube, watching the little flow guide so as not to breath too quickly.
Coughing is to be expected(and encouraged). Try to slowly increase your volume to ~ 1200-1500 cc/br.