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

The answer to your question is below:

Explanation:

Density: is the ratio between the mass of an object and its volume.

              density = mass/ volume. Its units are g/ml, g/cm³ or kg/m³.

What does it tell you about the substance?

Density tells the degree of compactness of a substance. It could tell if the substance is solid or it is porous.