Section 7.2 PAGE STYLES of the
memoir manual describes the pre-defined page styles:
The page styles provided by the class
empty The headers and footers are empty.
plain The header is empty and the folio (page number) is centered at the
bottom of the page.
headings The footer is empty. The header contains the folio at the outer
side of the page; on verso pages the
chapter name, number and title, in
slanted uppercase is set at the spine
margin and on recto pages the section
number and uppercase title is set by
the spine margin.
myheadings Like the headings style the footer is empty. You have to
specify what is to go in the headers.
simple The footer is empty and the header contains the folio (page
number) at the outer side of the page.
It is like the headings style but
without any title texts.
ruled The footer contains the folio at the outside. The header on verso
pages contains the chapter number and
title in small caps at the outside; on
recto pges the section title is
typeset at the outside using the
normal font. A line is drawn
underneath the header.
Ruled This is like the ruled style except that the headers and footers
extend into the fore- edge margin.
companion This is a copy of the pagestyle in the Companion series
(e.g., see [MG+ 04]). It is similar to
the Ruled style in that the header has
a rule which extends to the outer edge
of the marginal notes. The folios are
set in bold at the outer ends of the
header. The chapter title is set in a
bold font flushright in the verso
headers, and the section number and
title, again in bold, flushleft in the
recto headers. There are no footers.
book This is the same as the plain pagestyle.
chapter This is the same as the plain pagestyle.
cleared This is the same as the empty pagestyle.
part This is the same as the plain pagestyle.
title This is the same as the plain pagestyle.
titlingpage This is the same as the empty pagestyle.
EDIT: You can see them in action using this simple document
Each group of four pages illustrates one style (I didn't include the
myheadings style); the
background package was used to inform the corresponding style that is being used.