Question

What is density? What does it tell you about the substance

Answer 1

it tells you the ratio between the two of them.mass(weigh) and volume (takes up space). compares other substances with the amount per unit size of the substance

Answer 2

(1)Density is the degree of compactness of a substance.
(2) Density is the degree of consistency measured by the quantity of mass per unit volume. 

basically, density is mass spread out over volume. Some examples are oil and water. Oil is more dense than water so it rises on top of the water when they come in contact like in oil spills.