@ Sandeep Sharma,
Natural gemstones are a part of nature and are formed due to concentration and crystalization of particular chemicals and minerals (under the earth cover) over many years.
Human body again is a part of nature. Any disease caused in the human body is an imbalance of chemicals and minerals.
Wearing appropriate gems (of recomended sizes) can help in recovering and fully healing oneself. In certain cases, gems are either burnt and their ashes are consumed (in very small proportions) to heal faster. But such therapy has to be obviously performed under an advise of a specialist.
Wishing you good luck, may God bless you and above all?