These are van der Waals interactions. This is the effect of the charges on the atoms have on molecular conformation. It is an optional term in most force fields. The dielectric constant is a term to describe how polar a solvent is. Water has a dielectric constant of 80 and benzene has a dielectric constant of 2.
Charges have a much greater affect in a polar solvent than in a non-polar solvent.
During the optimization process the components contributing to the energy are calculated. Those making the greatest contribution to the energy are changed in order to make the energy fall. The energy is again calculated. The structure is then said to be optimized. It is frequently necessary to optimize several different conformations to get a realistic idea of which is the lowest energy conformation of the molecule.