Basics
What is Charge?
Charge is a fundamental property of matter. It is that fundamental property of matter, due to which a matter experiences a force when placed under an electric or magnetic field. Charge is denoted by $q$ .However, some also use capital $Q$ to denote charge. Actually, we generally use capital $Q$ to denote macroscopic charges and small $q$ to denote microscopic and infinitesimally small test charges.
Presently, you are not familiar with the terms- electric field and magnetic field. But we can understand them below deeply.
Consider we get any point sized particle charged by whatever possible method (we will discuss the methods of charging later). Say for now, the point sized particle has got a charge of $-12 C$ {Charges are measured in Coulomb (we will learn it later)}.
Charged particle in Electric Field :
Let's say we have switched on a uniform electric field of 1.5 Newton/Coulomb or 1.5N/C. It would mean that each stationary & charged particle kept in this electric field would experience a force of 1.5 newtons per each coulomb of magnitude. The direction of the force will be dependent of nature of the charge. For positive charged particles, it would move or tend to move in the direction of electric field. But for negative charged particles, the force will be exerted in a direction opposite to electric field.
Now, if we put our assumed charged particle of $-12C$, then after calculating it would experience a force equal to 18 newtons in a direction opposite to the electric field.
1 Coulomb charge $\to$ 1.5 newtons of force
$\therefore -12$ coulombs charge $\to$ $-12 \times 1.5$ newtons force $\;=\; -18 N$ of force
Negative sign shows opposite direction to electric field.
