A hypothesis is an integral part of the scientific method. Simply put, the scientific method gives us a uniform way of examining and evaluating things. Within the scientific method we 1) gather information, 2) create a tentative answer, 3) create a testable prediction, 4) experiment, and 5) conclude what we learned. What we learned will either support or not support the tentative answer (#2). If we performed the process correctly, others will be able to repeat our experiment and achieve the same results. 

In text books it looks like this:

    1) Observe
    2) Hypothesis
    3) Predict
    4) Experiment
    5) Conclude by supporting or not supporting the hypothesis in #2