First off, you have to apply online. expect to take at least 1.5 - 2 hrs on the application. If you apply to a big hub, they will usually give you an interview and a tour of the facility, but don't get too happy, that doesn't mean you're getting the job. The H.R. personnel will then take everyone in to a meeting room to kind of talk amongst yourselves while he/she pulls one person at a time into his/her office for a 1:1 interview. That will conclude the first day.
If they want to hire you, they will call you back. Then you'll have a week of training and go over rules and safety regulations. It's extremely tedious, but you get paid. UPS is BIG into safety and you will have to take quizzes over the videos and material you cover, so pay close attention. You cannot start work until you have passed all quizzes and tests. Keep in mind that the videos are NOTHING like loading/unloading in the trailers. The videos make it seem easy and clean... The videos are from the truth.