Smell … a marvelous sense

Smell is a very direct sense. In order for you to smell something, molecules from that thing have to make it to your nose. Everything you smell, therefore, is giving off molecules -- whether it is bread in the bakery, onions, perfume, and a piece of fruit or whatever. Those molecules are generally light, volatile (easy to evaporate) chemicals that float through the air into your nose. A piece of steel has no smell because nothing evaporates from it -- steel is a non-volatile solid.

When you smell many fruits or flowers, what you smell is esters evaporating from the fruit or flower.