The Multiple Y-Axis feature is available on Bar, Line, Area and Scatter (No Aggregation) charts. You can assign multiple columns to Y-Axis on those charts.
For charts that support Multiple Y-Axis, you see the plus ("+") sign right next to the "Y Axis:" label.
You can click that plus sign to add another Y-Axis to the chart.
You can click more to add more Y-Axises up to 5.
You can remove unnecessary Y-Axis by clicking the dropdown menu from on the target Y-Axis and selecting
Note that you cannot remove Y1-Axis.
You cannot assign multiple columns to Y-Axis and a column for Color at the same time. As soon as you assign multiple columns to Y-Axis, the column assignment for Color will be removed if there's any, and Color control will be disabled.
But you can still change the color scheme from the Color dialog. See Color section for the detail about Color.