A regression line in Excel is used as a way of visually depicting the relationship between the x and y variables in a graph. It shows the general trend of the data points.
A regression line can be created in Excel by going to the data tab and clicking on data analysis. If this button is not available, the Analysis ToolPak needs to be added. This can be found under the Add-Ins tab of the Excel options menu. Select regression from the list and click ok. Select the y range and then the x range. Check the boxes labeled residuals and labels. Select an output range and click ok. The R value indicates the percentage of data points that fit on the calculated regression line.