You must compare each word individually, it is not possible to use a semicolon-separated list.
E.G.
Begin Condition : [{LASTSPOKENCMD}] Contains 'Confirm' OR [{LASTSPOKENCMD}] Contains 'Affirmative' OR [{LASTSPOKENCMD}] Contains 'Yes'
You can use the condition builder when creating the condition initially, by selecting "Compound Condition Builder" instead of "Single Condition", or you can edit an existing condition by right-clicking it and choosing "Edit With Condition Builder" in the context menu.