The smell of something is a quality it has which you become aware of when you breathe in through your nose.

Your sense of smell is the ability that your nose has to detect things.

If something smells in a particular way, it has a quality which you become aware of through your nose.

If you say that something smells, you mean that it smells unpleasant.

If you smell something, you become aware of it when you breathe in through your nose.

If you smell something, you put your nose near it and breathe in, so that you can discover its smell.

If you smell something, you feel that it is likely to happen or be true.