The net charge is the sum of all charges. The free charges are the electrons that can move freely through the conductor.
Work Step by Step
The net charge on a conductor is the sum of all of the charges in it. If the conductor has more electrons then protons, the net charge is negative. If the conductor had electrons removed from it, so it now has fewer electrons then protons, the net charge is positive. If the conductor has equal numbers of positive and negative charge, the net charge is zero. The free charges in a conductor are electrons that are mobile; They are only loosely bound to their original atoms, and move freely within the conductor. A conductor can be neutral, i.e., have zero net charge, but have lots of free charges.