What is the main idea of an experiment?

An experiment is a set of observations performed in the context of solving a particular problem or question.

In scientific inquiry, an experiment (Latin: ex- periri, "to try out") is a method of investigating causal relationships among variables. An experiment is a cornerstone of the empirical approach to acquiring data about the world and is used in both natural sciences and Social Sciences. An experiment can be used to help solve practical problems and to support or negate theoretical assumptions. To test the hypothesis stated prior to designing and carrying out the experiment. That is, you run experiments to test out a question you have. someone else's Example:

Hypothesis - Eating cake 3 meals a day will make you gain weight.

Experiment - Weigh yourself. Eat cake 3 meals a day for X amount of days. Weigh yourself afterwards.

Conclusion - Eating cake 3 meals a day will/will not make you gain weight.