All the basics
Light Source and Rays: Suppose there's an object in front of a plane mirror, and there is a light source illuminating the object. Light rays travel in straight lines from the object to the mirror.
Reflection: When these light rays encounter the smooth surface of the plane mirror, they undergo reflection. According to the law of reflection, the angle of incidence (the angle between the incident ray and the normal to the mirror surface) is equal to the angle of reflection (the angle between the reflected ray and the normal).
Virtual Image Formation: The reflected rays converge as if they are coming from a point behind the mirror. However, no actual light converges at that point. This point is called the virtual focus or the virtual image of the object.
Size and Distance: The virtual image formed in the mirror is of the same size as the object, and the distance of the virtual image behind the mirror is equal to the distance of the object in front of the mirror. The image appears to be behind the mirror, but it cannot be projected onto a screen.
Laterality: The orientation (left-right reversal or laterality) of the image is reversed in a plane mirror. If you raise your right hand in front of a mirror, your reflected image appears to raise its left hand.