I have a friend who have boils spots on back an buttocks, some inflammed. Can u tell me how and y these come about?

From bacteria. Most 'boils' are due to staphylococcus bacteria infecting the skin.Pus forms below the skin which swells to form a painful boil.Sometimes streptococci & pseudomonas may cause boils.Often the 'boil' can be cured by a special drainage procedure performed by your doctor.If the surrounding area is red & angry antibiotics are needed. If untreated the infection can spread to the blood & become dangerous.
May be acne. These may be acne with blocked hair follicles that develop purulent inflammation.