Cubed trailer

Not knowing your supervisor, it is hard to say. But wouldn't be surprised if @JPenn is exactly right.
Look, I'm not tryin' to bust your balls here. Only you can decide if you are able to do the job safely or not. If you KNOW you are not, then find another job. (I know, that is much easier for me to say, sitting here on my fat backside, than it is for you to do, but it is the truth.)
OTOH, if what you need is somebody to show you how to do something, then don't be afraid to ask.
So you approach your boss. Don't say this load is dangerous and against OSHA rules, as he will undoubtedly tell you where to place OSHA. Say something more on the order of, "I don't know how to get this first stuff off the truck without DAMAGING THE FREIGHT." Can you give me some ideas on how to do it, safely? Nobody wants to see their product damaged.
Merely a suggestion, but it is how I would handle it.
Oh yeah, if he tells you to pound sand, then you should just head to the beach!

 

Any company you go to is going to train you. Sysco, Gordon's US they all have training regiments there not going to throw you the keys to a truck with 20,000lbs on it and say go get em you'll be fine. Well they kind of did with me, but not 100% I had a guy with me who was on the light duty list so I wasn't really technically alone.

GFS our guys get trained for 3+ weeks actually it's a long while before you get really cut lose on your own, and you'll work with veteran drivers who have been around for 20 years and they will show you some tricks and stuff.

 

Yep. One of our brand new trailers. Actually has the logo branded in the wood floors...

It has been both, on occasion. Mostly a hand truck though...due to the wheels it makes a scary ladder.