Different hospitals do this differently but likely you will train with ideally one person and their relief for a minimum amount of weeks. It may be more people than that, but hopefully not too many more than that. Generally, you will watch them do what they do, then you will quickly progress to doing it with them at your side and then, more and more, on your own with them checking your work.
Unit clerk is a highly responsible position because you are arranging for doctor's orders to be implemented. Omitting or ordering the wrong thing has ramifications. Your work is ALWAYS signed off by an RN. The good news is that you create a system of check-off and then you become a slave to it. _No one is going to throw you into this and expect you to do it tomorrow_. These tasks are interleaved with phone answering and contending with families, since you often are the person "just" sitting at the desk.
As a student nurse, one of my favorite instructors said to me, "Don't let people interrupt you when you are giving meds because it is such an important task." This is true for UC's, too. You have to create some limits around yourself so that you can concentrate on the important task at hand and yet you will get input from those around you. It is a learned balancing act, so watch your mentors to see how they do this.
As for, "I'm not even sure I can find my unit." I worked in the 200 bed hospital that I had trained in for 5 years, then I migrated to the big, tertiary 700 bed hospital. Frankly, at the big new hospital, I carried a map of the hospital in my pocket for a long time. They had them for the visitors and I got one for me! Ask people for help. You'll learn soon enough.
take the pressure off of yourself of expecting instant perfection. They are hoping for steady progress not instant perfection. Also, the HR lady is paid to determine whether an applicant had the wherewithall to do certain low paid but highly responsible
jobs. The ability to successfully complete a pre-nursing curriculum says something about people and so she's taking a chance on ya. Yep, you'll get a crash course in medical terminology and I've even seen UC's in training carry cheat sheets or lists of terms that they needed to know but had trouble remembering.
And finally, in an ED I worked, we had a sign up that I thought, at first, had been placed there just for me, but I soon learned that it was a long term part of the decor. It said, "Please ask the stupid questions. They are easier to cope with than the stupid mistakes." Ask questions. It is expected.
Good luck. You obviously care about doing well and that in itself is a tremendous asset.