The slug name is the yellow messenger identifier for the journeys and can be used in the code to refer to the journeys.
When you specify “connecting quick replies to a journey”, I am assuming you want to go onto a journey when you click the quick reply. The “text” should be provided with the utterance of the journey to which the flow should be passed after clicking on that option.
More info here: https://yellowmessenger.atlassian.net/wiki/spaces/docs/pages/298385432/Response