For example, If you have already introduced the author and work from which you are citing, and you are obviously referring to the same work, you probably don't need to mention them again.
However, if you have cited other sources and then go back to one you had cited earlier, it is a good idea to mention at least the author's name again (and the work if you have referred to more than one by this author) to avoid confusion.
Whenever you change the original words of your source, you must indicate that you have done so.
Otherwise, you would be claiming the original author used words that he or she did not use. You could accidentally change the meaning of the quotation and falsely claim the author said something they did not.
But often you can just tag this information onto the beginning or end of a sentence.
For example, the following sentence puts information about the author and work before the quotation: Milan Kundera, in his book The Art of the Novel, suggests that “if the novel should really disappear, it will do so not because it has exhausted its powers but because it exists in a world grown alien to it.” You may also want to describe the author(s) if they are not famous, or if you have reason to believe your reader does not know them.
However, just skipping it would not work -- the final sentence would not make sense without it. In order to do so, you will need to use some editing symbols.
Your quotation might end up looking like this: In his essay, “United Shareholders of America,” Jacob Weisberg insists that “The citizen-investor serves his fellow citizens badly by his inclination to withdraw from the community. by focusing his pursuit of happiness on something that very seldom makes people happy in the way they expect it to.” The brackets around the word [money] indicate that you have substituted that word for other words the author used.
To make a substitution this important, however, you had better be sure that [money] is what the final phrase meant -- if the author intentionally left it ambiguous, you would be significantly altering his meaning.
That would make you guilty of fraudulent attribution.