Pearson's correlation coefficient measures the strength and direction of the relationship between two variables. To begin, you need to add your data to the text boxes below (either one value per line or as a comma delimited list). So, for example, if you were looking at the relationship between height and shoe size, you'd add your values for height into the X Values box and the values for shoes size into the Y Values box (or vice versa).
When your data is in place, and you're ready to do the calculation, just hit the "Calculate R" button, and the calculator will run various tests on your data - to make sure it is suitable for the Pearson statistic - and then spit out the correlation coefficient, together with a lot of detail about the calculation.