Atoms are made of protons, neutrons, and electrons.
Every electron has a small negative charge (-).
The proton has opposite charge i.e., positive (+).
Neutrons are electrically neutral and have no charge.

The protons and neutrons are present in the center of atoms forming what is called the nucleus and the electrons revolve around them.

It is important to remember that particles, which have same charge repel while unlike charges attract each other. Therefore a proton and electron will attract while a proton and proton will repel each other. In other words they will move away from each other. Electricity is the flow of electrons so it is necessary to measure the charge. The basic unit for measuring charge is the coulomb or the letter C.

1 coulomb =  6,250,000,000,000,000,000 electrons