I taught neuropsychological research with an emphasis on special education for 25 years. I got started in this area when I told a friend that I did not have visual imagery. Her reaction was, "How do you think?"
I think by talking to myself but she thought via mental imagery. From there I developed a theory of the causes and remediation of reading disability.
To get started, try a simple experiment. Image an animal. Now rate it from 0-10 in terms of vividness and being lifelike. Did you image with your eyes open or closed? Now image with your eyes closed if they were open or open if they were closed. Now rate the image. Did it change?