A mammogram is an x-ray of the breast. The test is used to look for breast disease in women who appear to have no breast problems. This is called asymptomatic (without symptoms). Asymptomatic women usually have screening exams. This exam is usually limited to two x-rays of each breast. During a mammogram, the breasts are pressed between two plates to flatten and spread out the tissue. This is called compression and is necessary to see all the tissues and reduce the levels of radiation necessary to get a good picture.
A technologist (usually a woman) will position you correctly for the exam and take the pictures.