If you want to combine more than two different data series with common horizontal and different vertical values, you could not just add another axis to the chart. You need to combine several charts into one chart.
If you have several parts of something whole, you can demonstrate each item in one pie chart. But, when several parts each amount to less than 10 percent of the pie, it becomes hard to distinguish the slices.
If you have several parts of something one, you can demonstrate each item in one pie chart. But sometimes you want to demonstrate the changes of those parts and doughnut chart will help you to do this.
Some function in Excel is available only when the add-in is installed. For example, Solver or the Analysis group is not avalible in standard ribbons, you need to install the add-in before you can use it. See also Using Solver.