What is the difference between disability and disorder?

Simply put a disorder can cause a disability.

A disability (meaning impaired, as in physical functioning) is a physical or mental impairment that prevents an individual functioning as most people could.

A disorder (an ailment that affects the function of mind or body) is the name given to a disease which may sometimes manifest in such a was as to cause a disability. Not all disorders (eg an eating disorder) cause a disability