A controlled experiment is a scientific test that is directly manipulated by a scientist, in order to test a single variable at a time. The variable being tested is the independent variable, and is adjusted to see the effects on the dependent variable.
The scientific method uses controlled experiments but it begins with an observation, which leads the scientist to ask a question. The scientist then proposes a hypothesis, a testable explanation that addresses the question. Controlled experiments are then carried out to test the hypothesis. Observations from the controlled experiment might then lead to a refined hypothesis and the cycle continues.