Next to the Category
Groups field, click Add or Edit to open the Group Properties dialog.
Enter the name of the data you want to plot on the X axis.
Specify this information:
Label
Type a label for the X axis data or click the
browse button to open the Enter Field/Expression dialog
where you can select a label. This label is the legend that describes the
data.
Group on
Click Add to open the Enter
Field/Expression dialog where you can select the data field,
shown on the X axis, for grouping the data plotted on the Y axis.