If you do have historical responses available, you'll see them on the right-hand side when you click on a question.
The search engine reads your question, looks in your Knowledge Base, and shows relevant matches. You can scroll down the window on the right-hand side and see all of the possible options.
If you are preparing a free-form response to a question and you find a match, you can click Use Response. Your entire response from the Knowledge Base will be copied into your response area.
If you write new and unique responses, the switch on the right side to 'Write to Knowledge Base when approved?' will be selected as Write. This means that your approved responses will be saved to the Knowledge Base so you can use them again.
Next: See what the Workflow controls do.