Simply place the entire heat pack in microwave for 2 minutes to provide a therapeutic heat or cool it down in your freezer to create a cold pack.
Dimensions are roughly 11"x6"
If the cover gets soiled, it is best to spot-clean it with a damp cloth. Provided the grain inside doesn't get significantly wet it will probably be fine to let the cover air dry. Or use a hairdryer to dry the spot if in doubt.