Parameters are most commonly file names. A parameter needs a space in front of it. Some sentences do not need a parameter as the VAX has built-in defaults. Some sentences need a parameter and if you don't type one in, the VAX will prompt you for one. 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.