You will see "slideshow" listed at the top of your AwesomeBox group page. However, after the box closes, you won't see this option, but all you do is click on any card thumbnail and the slideshow will pop up.
If the AwesomeBox is finished, then simply click on any card and a carousel will pop up to click through all the cards and songs.
The slideshow feature is a carousel format. You can click to the right to advance through the cards. Any song that may have been added to a card will start playing with that card. A sample of the song is played rather than the full track due to limitations with the Spotify API.
The slideshow cannot be autoplayed in fullscreen and dissolve between images like you might normally see at a party or gathering, but you might still have success using a projector to show your computer screen and scroll through the cards for everyone in a room to watch together.