This is just how it worked for me; YMMV.
If I recall correctly, it was 3 to 4 hours (paid). You sit around, watch a few videos that were made about the same time that Bill & Ted's Excellent Adventure came out, do a few stretches, and sign a stack of papers. The HR person should explain the basics of how the health coverage works, union locals, etc; they will also answer some questions.
The orientation I attended got a brief tour around a facility, and I remember thinking "This is surreal; boxes on belts and all manner of silliness."; plus, current employees look at you like your a deer in the headlights - which I sort of understand now.
Good luck, and enjoy preload.