Bot speaks card is used to create bot (Alexa echo dot) response. Bot can reply with dialogue and can play MP3 music as well. Each dialog consists of turns between your user and Alexa. End session in bot response will end the Alexa conversation dialog.
The highlighted blue box in the image End Session toggle button is to end the user dialog conversation. To add music to the conversation, use upload music files and paste the URL in the input box.