Sense of Smell
Sense of Smell is how your nose picks up tiny bits floating in the air around you.
Think of it this way
When you bake cookies, tiny bits of sugar and butter float off the tray into the air. These bits drift around the kitchen and land in your nose. Your nose has small spots that catch each bit, like a tray with many small cups. Each cup fits only one kind of bit, and when it fills, your brain gets the signal.
Explaining sense of smell by grade level
Your nose can smell a flower from far away. Tiny bits float off the flower and go into your nose. Your brain then tells you what the smell is. Some noses are better at this than others.