The basics (assuming you're covered by the central):
-If you're on the schedule, and you get to work on time, you're entitled to 3.5 hours of work. If the work doesn't exist, they can pay you to go home. Use caution, though. If I was a supervisor, I'd hand you a broom. I'm sure I'm not the only one.
-If you aren't scheduled for 5 days in a week, and there's a sort happening on the weekend, you are entitled to that work before somebody who has already worked 5 days.
-You are entitled to a 10 minute paid break.
-If you're laid off for more than a week, you can bump a less senior employee on another shift until your shift needs you back.
-Supervisors aren't allowed to perform union work except when training and/or they've exhausted all options (which they rarely do).
-Supervisors aren't allowed to harass you.
-If you're fired or suspended for a non-cardinal infraction, you can continue to show up to work regardless of what the schedule or your supervisor says until your termination or suspension is upheld at a local level hearing.
My contract is hundreds of pages long, but this is a pretty good start if I do say so myself.