This starts a new sentence. Should be a period, followed by a capital letter:
"... user form, that information..." should be "... user form. That information..."
"I am trying to create a userform that will copy the narrative from main document in the selected cell and place the text into a textbox within a userform so that the user can edit" is a statement, not a question, and so should end with a period, not a question mark.
(Trying to be helpful...)
What environment does this apply to? Is this Excel? VB6? VB
.NET? Access? Word (if so, which version)?
If you are using Word, the Selection object should have in it the data you are after.
The word you used, "main document," implies Word, but the description ",in the selected cell," seems to imply Excel. If you could clarify, that would be helpful.