Electrons, protons, neutrons
All bodies around us are made up of electrons, protons and neutrons. In many cases, the number of protons and electrons is not the same (the body is not electrically balanced).
If a body has more electrons than protons, it said that it is negatively charged and if it has more protons than electrons, then it is positively charged. When the number of protons and electrons is the same, there is no charge or the body is neutral (the body is not charged). The following diagram shows two bodies with no charge (It is a neutral body).
In order for a body to be charged, either positively or negatively, it has to be affected in some way. One way to alter the body (assuming a metal body) is to heat it. In this case, the body gets more or less electrons, and the number of protons remains generally constant.
When electrons pass from one body to another, the body that loses electrons is positively charged and the body that gains electrons is negatively charged. This movement of electrons is called electric current.
Metals allow an easy flow of electrons. This flow may be due to the action of electrostatic forces. When this happens, we say that the electrons are under the influence of an electrostatic field, also called electric field.