That is, correlation does NOT imply causation. It does not, because is there could be some other third variable causing both of the phenomenon that are covarying. Before you select your study method, you must have a statement of inquiry. That is a statement of what you think your study will find. That statement is a hypothesis.
Hypothesis is related to hypothetical.
A hypothesis is a statement of what your study results might be. The hypothesis will be tested using inferential statistics. Based on the outcome of those inferential statistics, you will decide whether your hypothesis is consistent with the data you collected. Some people suggest the primary activity of science is hypothesis testing. In stating the hypothesis, the variables of interest need to be clearly defined.