The VAX will keep asking you for a filename until you cancel the command or type a filename in. Some sentences can have a qualifier. That tells the VAX to do the command but do it slightly differently than normal. A Qualifier restricts or modifies the command. Qualifiers need a slash in front of them.
Some sentences require more than one parameter.
If you don't type the parameters, the VAX will prompt you for both of them. If you make a mistake, and the VAX doesn't understand your sentence, it will give you an error message. The error message looks confusing, but it is giving you a hint as to the problem. It will type part of the sentence between slashes. This is the VAX's way of highlighting the problem.