The normal force is one which prevents objects from 'falling' into whatever it is they are sitting upon. It is always perpendicular to the surface with which an object is in contact. For example, if there is a crate on the floor, then we say that the crate experiences a normal force exerted by the floor; and because of this force, the crate does not fall into the floor. The normal force on the crate points upward perpendicular to the floor.
It is called the normal force because “normal” and “perpendicular” mean the same thing.
The normal force is always perpendicular to the surface with which a body is in contact. For a body on a sloping surface (say a ramp) the normal force acting on that body is still perpendicular to the slope.
Let's add the normal force to our FBD and represent the normal force with the letter N.