Hi Jess,
We know that the radius of the Earth is about 6400 km and that the radius of the Sun is about 695500 km. The volume of a sphere is 4/3 x pi x radius^3, or the radius "cubed" which is just the radius x radius x radius. Pi is just a constant we use in geometry and physics and it is 3.14159. You can use this formula to calculate the volume of the Earth and the Sun. Then, you can divide the volume of the Sun by the volume of the Earth. When you do this, you find that the volume of the Sun is about a million times larger than the volume of the Earth.
Kris