Your sense of smell is sensitive enough that you can use it as a supplement to sight and hearing in combat, as well as using it to track targets by the scents they leave behind.
If you have Scent as an Imprecise Sense, you gain Advantage on Survival checks to track a creature if you can catch their scent, and you can detect which square(s) a creature is in if it is within range of your Scent ability and not somehow prevented from emanating a scent.
Scent can only be gained as a Precise Sense by monsters, and the rules for how they interact with their sense of smell differ on a case-by-case basis.