The pathway of air in our body through the respiratory system 

 Nostrils → Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Lungs → Alveoli.

By respiratory system, we usually mean the passage that transport air into the lungs and to the microscopic air sacs called alveoli and vice versa

The inhaled air passes through the nasal cavity its temperature is brought close to that of the body, and it takes up water vapour from it. Air is also filtered in the nasal cavity. 

Epiglottis, a flap-like muscular valve controls movements of air and food towards their respective passages.

When air passes over the vocal cords in the larynx, it causes them to vibrate and produce sounds.

The trachea or windpipe channels air to the lungs and it divides into two bronchi – one leading to each lung.

The bronchi further divide into small and smaller branches called bronchiole

Bronchioles finally terminate in clusters of air sacs called alveolus in the lungs which are very small and numerous.

The gaseous exchange takes place in alveoli as blood capillaries take up oxygen and expel CO .

Breathing is the process of inhaling and exhaling. 

When the volume of the chest cavity is increased, its internal pressure decreases and the air from the outside rushes into the lungs. This is known as inspiration.