Smear tests protect women against developing cancer of the cervix
This is because, before cancer develops, the cells in the cervix undergo changes which are sometimes known a pre-cancerous changes. If undetected an untreated these changes can develop into cancer over several years. They cause no symptoms so the only way to detect the changes is to have regular smears. Seven in every hundred smears will be abnormal. A smear is a screening test, not a diagnostic test. In other words an abnormal smear result suggests there might be an abnormality on the cervix.
You will be referred for colposcopy to determine if there is indeed an abnormality and whether it requires treatment.