Humans have central lungs in a thoracic cavity attached to a trachea, pharynx, and internal and external nares. The alveoli are surrounded by a net of capillaries where the oxygen and carbon dioxide are exchanged with the blood. The blood then transfers the oxygen to the cells via a closed circulatory system.
Insects on the other hand, contain a vast network of trachea extending throughout the body. The trachea comes into contact with the outside via small holes in the segments of the exoskeleton called spiricles. The insect uses its abdomen to take in oxygen and release carbon dioxide. Since they have an open circulation there are no capillaries so the oxygen is transported via a material called hemolymph to the cells.