Hi Phyllis: Sandra's explanation is absolutely correct!! Thanks Sandra...
Here's the World Health Org's definition on t-scores. Your score falls into what they categorize as established osteoporosis. Have you had a fracture? If not that's great, but you need to speak with your Dr to find a good treatment along with the recommended supplements and exercise.
Since your score is low, I would ask your Dr about seeing a Physical therapist, that could give you an evaluation and personal work out plan that would be safe for you that doesn't involve any risky movements, like bending, twisting, strecthing from the waist.
Good luck finding out what is best for you!