Imagery is the use of figurative language to represent objects, actions and thoughts in a way that activates the physical senses of the reader (sight, smell, hearing, tactile and taste). It is what makes the reader involved in a story, by activating feelings he/she might know. It is what makes a story feel realistic.
Its function in literature is to create a graphic representation of a scene, with as much description as possible so the reader can paint a mental picture of what's going on.
So, that through the use of imagery meaning is created could mean that it is what gives a story depth and complexity, it is what makes a story similar to the real world.