What do chiropractors do in arthritis therapy?

Little. Chiropractors use an outmoded, ancient idea as a theoretical basis for treatment. The use high powered x-rays to find "subluxations" of the spine as a cause of all illness. They provide a deep massage which might give temporary relief but no cures. They cannot treat arthritis with these ideas and are more than likely to aggravate and worsen this condition. See your rheumatologist.
A lot! They manipulate your joints to maintain flexibility and strength, they may apply heat. They also teach you exercises to do at home and many are qualified to discuss different helpful supplements with you. One thing they dont do is write prescriptions!