Let's use the example of the burning match to help us understand how this sense works. Here is how your nose works. When the match started to burn, tiny little particles of ash that came from the match floated through the air. These small pieces of material are too small for us to see, but the nose is sensitive to them and can smell them as they travel through the air into your nose. We don't always smell an odor right away because it takes time for the small particles to travel in the air and then into your nose to the nerve endings.
Human beings have a very weak sense of smell.
As people evolved and began to use reason more, they didn't need to smell things quite as well as other animals did. They could use their eyes and their brains in a different way. There is one way your sense of smell is different from all your other senses. After sensing a particular smell for a while, your sense of smell gets tired. When you first come into the house, you can smell dinner cooking, but after that your olfactory nerves get overtired and then you don't smell anything at all.