A plane mirror is a flat, smooth surface that reflects light in a regular way. The picture demonstrates how light is reflected off of the mirror with equal angles of incidence and reflection (the Law of Reflection states that the angle of incidence equals the angle of reflection). At the point where the dotted lines intersect is the image. When the image appears to be behind the mirror, there is a virtual image. There is a real image produced if the light rays actually converge and pass through the image.
A lens is a transparent material with a curved surface that bends or refracts light. Refraction is when light rays change direction when passing from one medium to another. Lenses may be concave or convex. If the object is at 2F, the image would be at 2F(which would be the same size, inverted). If the object is F, there is no image. If the object is between F and 2F, the image is greater than 2F(which would be enlarged, inverted). Convex lenses produce virtual images also. If the object is placed in between the focal point (F) and the lens, a virtual image is formed. The images are erect (it is not upside down) and enlarged. Concave lenses form virtual images. These images are erect and reduced in size.