Hi Ralph!
Thanks for using Excel for the iPad. And thanks for your question.
In Excel for iPad you can edit the source data for your chart by directly editing the values in the cells in the spreadsheet just like on desktop versions of Excel. You can also change the source data range (e.g. adding a new series) by manipulating the colored highlight borders that appear in the spreadsheet when a chart is selected. But you cannot make changes to the category labels or the series names directly in the chart.
However, you should be able to get the chart you want by forming your source data with series names and category labels, then using the Recommended chart command on the Insert tab.
Let me know if this doesn't quite answer your question.