Check icon in Android Auto

[jamesckirk]

I am using the Android Auto app on my smartphone to connect to Spotify inorder to play downloaded songs for my drive.  It works great mostly, but the one icon I cannot figure out is the checkmark, then the plus sign that shows after I select that.

Can someone answer me what each of these are for?  Also, some sort of visual diagram would be great for this.  As a new user I did not find this app intuitive as with other apps within Android Auto.

Thanks for your assistance!