A difference between a theory and a fact is a theory explains observations, and a fact is something which is believed to be true. A good theory has to fulfil two requirements. It must accurately explain a large class of observations on the basis of a model that contains a few elements, and it must make definite predictions about the results of future observations.
So the theory of evolution describes how evolution occurs, but shouldn't there also be a law then which states the conclusion of this theory? For example, a 'law of evolution' which says that over generations, species' genetic material changes, etc.. , and then a 'theory of evolution' which goes into more detail to explain how this occurs?