Sure, I will try to break this down into two high level options.
Option 1: Simply configure the QnA data, train the bot and let NLU handle answering on its own. This is good for cases where you just want the bot to respond appropriately without need to perform anything in custom way.
Option 2: Configure transition rules if you want to perform different actions on different intent values or any other attribute. Connect required nodes based on these conditions, and connect a node on otherwise which might call a custom action for example. Within that custom action you may handle all necessary conditions as you want.
To summarize, use transition rules only when you want to perform some custom action and use plain QnA based automated response capability if you want to ensure appropriate answers.