What do internists doctors do?

General medicine. For adults. I know it's confusing, but think of them as specialists in adult medicine that don't operate. The way pediatricians focus on children. Then they specialize on a particular organ system like the heart, the lungs, the kidneys.
Internists. Internists are trained to diagnose and treat a host of medical conditions in adults or refer them for surgical treatment if needed.
Adult medicine doc. Internal medicine docs specialize in adult health. Some internists also do well woman care. Some don't.