After you have gather background information and made preliminary observations it is time to formulate a hypothesis. A hypothesis is merely a tentative explanation proposed to account for the observed phenomena. You are speculating on how natural events will turn out, based on what you know.
Science is systematic in method because it seeks a system of prediction.
That prediction is the hypothesis. Any hypothesis selected or formulated must be testable. Experiments generally test hypotheses by testing the validity of the predictions or conclusions derived from them. The primary purpose of designing scientific experiments is to test the proposed hypotheses. It is important to know that hypotheses are never proven - they are either supported or not supported by the data from the experimental results.