Programming

Consult the documentation for myprog - whatever that is.

If whoever wrote it was kind enough to write a man page for it, then use man myprog, or an info page - use info myprog, otherwise read whatever documentation there is for myprog.

-d is an option to the program, and dictionary is an argument to that option. You're supposed to replace dictionary with, I presume, the name of a dictionary.

I'm closing this thread. Please read the documentation for the program you are referring to. If you need help understanding the general concepts then consult our man pages, which contain hundreds of commands, most of which take options just like "myprog" - whatever that is - does.