A picture is worth a thousand words. This wonderful image by Businessweek helps to convey the difference between correlation and causation in a much easier to understand manner as compared with standard research texts.
In other words, correlation enables prediction whereas causation enables explanation. Correlation denotes the strength of a relationship between two variables, while causation requires correlation of cause and effect, temporal precedence and rejection of alternative hypotheses.
Thus that correlation proves causation, or, cum hoc ergo propter hoc, is a logical fallacy.
See the original at Correlation or Causation? – Businessweek.