To add a class to your Queue follow these steps:
Go to the video page of the class you want to add to your queue.
Below the video player, click the + Queue button.
There is also an x in the upper right corner of each video in your playlists if you wish to remove a video.
To view your queue, click on your name at the top and then Queue.
In this view, you can change the order of the classes in the playlist by clicking the Re-Order This List button.
Finding My Queue on Mobile
In the menu, go to My Videos > My Queue