Volume of Solid Inside Ellipse

Find the volume of the solid that results when the region to the left of the y-axis and inside the ellipse $\displaystyle (x^2/a^2)+(y^2/b^2)=1$

$\displaystyle a>0$

$\displaystyle b>0$

a is not equal to b

It is revolved around the y-axis.

I don't know where to start or what equations to use or what to find. I'm further stumped due to the lack of numbers. Please help. Also, how would the problem change if it was revolved around the x-axis or to the right of the y-axis.

Thank you,

Derek