You need to have someone in the store explain your duties better. Also, when you don't understand something, ask someone to explain it.
As for "OS", all desktop, laptop, notebook, and tablet PCs use an operating system. So do many cell and prepaid phones. I believe some video/computer game systems also have operating systems, too, but have never had one.
Remember, just ask a question when you don't know the answer. Also remember, we on the spectrum are all:
A Different Drummer
If a man does not keep pace with his companions,
Perhaps it is because he hears a different drummer.
Let him step to the music which he hears,
However measured or far away.
--Henry David Thoreau