The CORREL function in Excel is used to calculate the correlation coefficient between two data sets. This coefficient is a measure of how closely two sets of data are related.

Here are the steps to use the CORREL function in Excel:

- First, select a cell where you want to display the result of the correlation coefficient.
- Type "=" followed by the word "CORREL" in the selected cell.
- Inside the parentheses, specify the range of cells containing the first set of data, followed by a comma, and then the range of cells containing the second set of data.
- Press Enter, and the result will be displayed in the selected cell.

For example, if your data sets are in cells A1:A10 and B1:B10, you would use the following formula:

=CORREL(A1:A10, B1:B10)

Excel will then calculate the correlation coefficient between these two sets of data and display the result in the selected cell. The correlation coefficient value will range from -1 to 1, where -1 indicates a perfect negative correlation, 0 indicates no correlation, and 1 indicates a perfect positive correlation.