They chose to work you or not. Some days they will and some days they will send you home with a hour pay. When they assign you a line some time you will stay with that line and other times you will be moved to a different line.
This place is terrible. They expect you to live at your job with little compensation and a huge amount of personal disrespect. The pay is almost the bare minimum of what they have to pay you. This versus their expectations on your job performance is hardly fair. One of the worse jobs that I've ever had.