What is the main thesis in Foucault's essay titled "What is an author"? Could anyone explain the aim of the essay?

This is the thesis (for what it is worth) -
look at the explanation below the quote and read the study guide links. Critical theory
is difficult and I find Foucault one of the most confusing. Reading Roland Barthes may
help you to understand Foucault.  I hope this
helps.

"It is obviously insufficient to
repeat empty slogans: the author has disappeared; God and man dies a common death.
Rather, we should reexamine the empty space left by the author's disappearance; we
should attentively observe, along its gaps and fault lines, its new demarcations, and
the reapportionment of this void; we should await the fluid functions released by this
disappearance," (121).

Foucault wants to discuss the
relationship between an author and a text, and the manner in which the text points to
the author as a figure who is outside the text, and who precedes the text (and creates
it). Eventually, Foucault will talk about the author as a Derridean "center" of the
text, the place which originates the text yet remains outside it. (Then, of course, he
will "deconstruct" that center/author).

In dealing with the
"author" as a function of discourse, we must consider the characteristics of a discourse
that support this use and determine its differences from other discourses. If we limit
our remarks only to those books or texts with authors, we can isolate four different
features.

First, they are objects of appropriation; the
form of property they have become is of a particular type whose legal codification was
accomplished some years ago.

Secondly, the
"author-function" is not universal or constant in all discourse. Even within our
civilization, the same types of texts have not always required authors; there was a time
when those texts which we now call "literary" (stories, folk tales, epics and tragedies)
were accepted, circulated and valorized without any questions about the identity of
their author.

At the same time, however, "literary"
discourse was acceptable only if it carried an author's name; every text of poetry or
fiction was obliged to state its author and the date, place, and circumstance of its
writing.

The third point concerning this "author-function"
is that it is not formed spontaneously through the simple attribution of a discourse to
an individual.