Short answers, pulled from the story.
The scientific method is an empirical method for acquiring knowledge through careful observation, rigorous skepticism, hypothesis testing, and experimental validation. It is an iterative, cyclical process whose core elements are characterizations, hypotheses, predictions, and experiments.
The scientific method developed from ancient and medieval practices, with early expressions of empiricism found in Aristotle, Epicurus, the Stoics, Alhazen, Avicenna, Al-Biruni, Roger Bacon, and William of Ockham. During the Scientific Revolution, Francis Bacon, Robert Hooke, Rene Descartes, and Isaac Newton shaped it further, and Newton postulated four principles forming the basis of modern science.
The term scientific method emerged in the 19th century, alongside institutional growth of science and new terms like scientist and pseudoscience. It came into popular use in the 20th century, helped by John Dewey's 1910 book How We Think and Karl Pearson's Grammar of Science from 1892.
In his 1975 book Against Method, Paul Feyerabend argued no description of scientific method is broad enough to cover all approaches scientists use. Physicist Lee Smolin's 2013 essay "There Is No Scientific Method" and historian Daniel Thurs in 2015 likewise treated it as a myth or idealization, though Karl Popper and others disagreed.
Between 1944 and 1953, the discovery of DNA's structure illustrated the scientific method's elements. Watson and Crick hypothesized a helical structure, predicted an x-shaped X-ray diffraction pattern, and confirmed it after Watson saw Rosalind Franklin's photo 51, then built their model using Chargaff's rules of base pairing and bond lengths deduced by Linus Pauling.
Falsifiability means a hypothesis must allow a possible outcome that conflicts with its predictions, otherwise it cannot be meaningfully tested. Karl Popper used falsifiability to demarcate scientific theories from non-scientific ones like astrology, stating that those unwilling to expose their ideas to refutation do not take part in the game of science.