To indicate means to point something out or to present evidence. If you feel sick during a car trip, you can indicate this to the driver by groaning loudly or announcing "I'm going to be sick!"
Scientists rely on data from experiments to indicate whether their theories are correct. Indicate can also describe a symptom or signal of something else. For example, a stock market recovery could indicate growing public confidence — or foolishness, depending on which expert you ask. The verb indicate comes from the noun indication, which in turn comes from the Latin word indicare, meaning "something that points out or shows."