Please explain me what is hairline fracture in ribs? And how to cure & take care of it?

"hairline" = "faint" Generally this term is used to describe a fracture that is just barely seen on x-ray. It will hurt just as bad as a fracture that is more easily seen, or mildly displaced.
Time. Rib fxs heal with time no matter how big. Pain meds and time and heat or ice.
Minor fracture. It is a break in the bone in which the fragments remain in position without any separation. Treatment is to avoid further injury ( avoid rough sports, etc ) and to control pain. You will be miserable when you sneeze or cough, but this should get better with time.