An insulator is a material in which charged particles are fixed in place. Practical conductors are often surrounded by insulators in order to confine the motion of charge to particular paths. The current through a wire is defined as the amount of charge passing through the wire per unit time. If the current consists of particles carrying negative charge, then the direction of the current is opposite the direction of the motion of the particles. Metals tend to be good conductors, while glass, plastic, and other non-metallic materials are usually insulators.
All materials contain both positive and negative charges.
In metals, negatively charged electrons can escape from atoms and are free to move about the material. When atoms lose one or more electrons, they become positively charged. Atoms tend to be fixed in place. Since the electron charge is negative, the current in a wire actually has a direction opposite the direction of motion of the electrons, as noted above. Fixed positive charge and negative charge moving to the right with speed in blown up segment of wire.