This is fine tuning the meta data the page title
and the site continuity so that it looks like a place people would like
to go when they are looking on a search engine for a subject.
There are programs that try to fool search engines and sometimes they do
a very good job but once they are found out the site goes to the bottom
of the list. Having other pages link to your site helps, so some
of the so called (SEO) programs will put a page up with links to your
site and this may bring you more traffic in the form of more spam mails
than you can ever deal with. And if the pages linking to your page
do not have any relevance to your material you get disregarded by
searches also. Paid keywords on search engine pages mean every time
someone clicks on a paid keyword the search engine charges a fee and
these are generally paid in advance. These paid placements are to
the side or top and often will not take you where you want to go. see
Search
engine optimization on wikipedia