Your union rep should be one of the first few people you talk to when you get to your facility. How much learning you get besides "here sign this and we won't wash you out" is up to your rep. Just joking. Kind of.
In all seriousness, we do a lot of bitching about the union on here but in general they are a positive influence on most facilities and do a lot of good for the workforce. I encourage everyone to join and I know very few controllers who aren't members, and i like to think it's not totally groupthink why we all stick around.