The basics of dual coding theory are that cognition includes the activity of two relating but different mental codes. A verbal code that has to do with language and a visual that is for non-language subjects, like mental images. They are different, however they’re connected with each other and work on their own. The verbal code functions more than the nonverbal in some instances and the nonverbal code functions more than the other at times but they are used together. During dual coding perception and memory are being used. Hearing, vision and touch in the case of language, and all five senses in the case of mental images are all used during dual coding.
Here is a video that can help you better understand on how dual coding works: