The queue is a way way to build a list of courses for later play.
To add a course to your queue, look for the plus sign and down arrow symbol:
It is available nearly everywhere a course title is listed.
Click the plus button to add the course to your queue. The plus button then becomes a checkmark.
Click the down arrow to see a pop-up menu.
You can also add a course to the queue here, or you can add a course to the top of your queue. You can also go to your queue from here.
You may also access your queue via the my courses pull-down menu near the top of the screen.