Dude, you can't possibly be this ignorant. I'm starting to think you're just a little troll asking all these dumb questions that could easily be answered by your "coworkers".
No idea how seniority happens. But, bring in burritos for your sort and transform into a mariachi singer for 15 minutes in the parking lot post-shift every day for 6 weeks and you will be granted honorary señority.
Dude, you can't possibly be this ignorant. I'm starting to think you're just a little troll asking all these dumb questions that could easily be answered by your "coworkers".
Seniority is something that just happens magically. It also depends on factors like what time of the year, your height and weight, your local supplement, and order of birth in your family.
I can tell you this: in my feeders department, buying lunch for your dispatcher and placing it discreetly in the car wash adjacent to the feeders department can buy temporary effects of increased seniority such as better job assignments and easy overtime. So I've seen.