When you get sick, your body generates antibodies to fight the disease and help you get better. These antibodies stay in your body even after the disease has gone, and protect you from getting the same illness again. This is called immunity, and you can be given a vaccine to develop it.
Immunization (or vaccination) protects people from disease by introducing a vaccine into the body that triggers an antibody response. The vaccine contains the same antigens that cause the disease, but the antigens in vaccines are either killed or greatly weakened. Vaccines work because they trick your body into thinking it is being attacked by a disease. Memory cells prevent re-infection when they encounter that disease again in the future.