To plot two columns against each other in Excel:

1. Select the two columns of data that you want to plot against each other.
2. Click on the Insert tab in the ribbon at the top of the screen.
3. Click on the Scatter chart type in the Charts section.
4. Select the type of scatter plot you want to create. The default option is usually fine.
5. Excel should automatically create a scatter plot with your two columns of data plotted against each other.

If Excel is still not letting you plot the two columns against each other, make sure that you have selected both columns of data before creating the chart. If that doesn't work, try switching the columns around so that the X axis data is in the first column and the Y axis data is in the second column.

I hope that helps!