I have studied and used linux for 2 weeks (!) and have been given this question:
How do you spell-check in Vi? You must spell-check from within Vi, with the corrected text replacing the original Vi text buffer contents. No saving the file, exiting Vi, and spell-checking the file separately!
I have looked in books and web info sites, and think it might be a redirection thing, although it says not to exit vi. I think the assignment is a push into getting involved in a forum because it's not easy for me to find the answer.