If you're a rookie or new to something, you could be described as callow — like callow freshmen in high school or the callow receptionist who can't figure out how to transfer a call.
The word callow comes from the Old English word calu, which meant "bald or featherless." It was used to describe young, fledgling birds. Over time, the meaning expanded to include young, inexperienced people. You'll most often see the adjective paired with the noun youth. Think of the callow youth as people who haven't tested their wings yet.