Science is both a body of knowledge and a process that gains information through observation, experimentation, and inference. Science follows rules, and its results are tested, revised, and retested until a great deal of confidence is reached in a particular conclusion (and even then it is still open to peer review and skepticism as new evidence arises - it is a process that corrects itself). These well-substantiated conclusions may then be referred to as a theory, as in the theory of evolution. Science answers questions such as "What is there?", "Where did it come from?", and "How does it work?", all in an attempt to learn more about our lives and our universe. The key is that science relies on evidence derived from observation, experimentation, and logical inferences. When faced with multiple possible answers, science prefers the most parsimonious explanation. Science is not a democratic process - truths are not found by popular vote, but based on evidence - the number of people who 'believe' in something is irrelevant (flat earth, geocentrism).
Nature of Science (Berkeley) - a step by step walk through of the nature and methods of science.