Sit or lie flat in a comfortable position.
Put one hand on your belly just below your ribs and the other hand on your chest.
Take a deep breath in through your nose, and let your belly push your hand out. Your chest should not move.
Breathe out through pursed lips as if you were whistling. Feel the hand on your belly go in, and use it to push all the air out.
Do this breathing 3 to 10 times. Take your time with each breath.
Notice how you feel at the end of the exercise.