Although benzene is often drawn with alternating single and double bonds (Kekule structure), this is not representative of what is actually going on. Refer back to the structure of a C=C double bond, which has two p-orbitals which overap to form a pi orbital. If you were to imagine three double bonds and their p orbitals on the six carbon ring or 'backbone' (comprised of 6 C-C single or sigma bonds) of benzene, you would have six p orbitals, one on each carbon, that all overlap with each other. This is represented as a circle within a hexagon. The electrons are said to be delocalised, meaning they are not confined to individual double bonds, meaning that benzene is planar. In 3D, imagine the planar hexagon with a donut (torus) above and below the plane to represent the six p orbitals overlapping with each other.