Can someone please explain specific gravity to me

my teacher just confuses me more and the book is really no help

Specific Gravity is another way to represent Density. We take the Density of water (usually) as equal to 1. Then other materials are the ratio of their density to density of water.

That is:

If something is twice as dense as water then its Specific Gravity = 2

By Dimensional Analysis the units cancel out and we are left with a "Dimensionless Unit." This is often very useful as it means that we do not need to convert units.

First answer is totally wrong.

Specific Gravity is a poor name. It is also called relative density, which is a much better name.

It is the density relative to that of water, very simply. It has no units and is the same in any system of units.

In the SI system, for example, water has a density of about 1000 kg/m³
The density of copper is 8960 kg/m³
so the SG or relative density of copper is 8.96 (no units)

Einstein described the "fabric" of space and time. He said that an object with mass bends the fabric and causes smaller objects that come close enough to fall toward it. Think of a fat man on a mattress next to his skinny wife. They both make an indentation in the mattress, but the man makes a bigger indentation so the wife falls in toward the man.

That's how gravity works. Throw a pen away from you and it seems to arc toward the ground. The truth is that the pen traveled a straight path through space and time, but the space/time fabric that it traveled through was bent by the mass of the Earth.

I hope that helps.