Well hopefully you got a tour of the facility so you will understand what is involved. I never did, but after two and a half years of working at my hub, I see new applicants walk around with a supervisor to get an idea of what goes on. It's a great time to change your mind.
Like Newbie said, could be any kind of package, any weight. It all depends on what route your drivers run. One of my drivers goes by an oil industrial plant and well...they need a lot of machinery parts...
It also depends on where you live, too many factors involved to give you a good answer. Just know it is less than 200 pounds because UPS freight will take care of that and not UPS ground. Although, I had to send a package back because it was longer than the truck it was designated to be loaded for.
I'm not sure what you mean by orientation, my hub has no such thing. Personally, I signed up online, went in for an interview, got a call next day from human resources saying that I had the job and to come in for work the following morning. First day I started working, 2 years go by I'm still on same shift, still working...
The only orientation for package handlers I know of is filling out a training packet when you start. They did this for 10 minutes after each shift my first week. Sometimes they make them watch a video, but I never had to.
Other than that, good luck! You are now a slave they will bend to their will...(Joking?)