First Law of Electrostatics:

The negative charge of the electron is equal, but opposite for the positive charge of the proton. Those charges are referred to as electrostatic charges. Inside nature, unlike charges (such as electrons and protons) attracts each other and such as charges repels each other. Those facts are known as the First Law of Electrostatics and are sometimes referred to as the law of electrical charges. This law should be remembered since it is one of the vital concepts in electricity.

A few atoms could lose electrons and others could gain electrons;  therefore,  it  is  possible  to  transfer electrons from one object to another. Whenever this occurs, the equal distribution of negative and positive charges no longer exists. A single object will hold an excess of electrons and become negatively  charged, and  the  other  will  become  deficient  in  electrons  and  become  positively charged. These objects, that can hold billions of atoms, will then follow the similar law of electrostatics as the electron and proton instance display above. The electrons which can move around inside an object are said to be free electrons and will be discussed in more detail in a later section. A greater the number of these free electrons an object contains, the greater its negative electric charge. Therefore, the electric charge could be used as a measure of electrons.