Does Wordpress CMS have its own search engine?
they have the on-site search feature, yes.
Yes you can search using WP. Read about it here: http://codex.wordpress.org/Function_Reference/get_search_form, and http://codex.wordpress.org/Creating_a_Search_Page
Absolutely not. Both the search on the front-side and in the admin panel leave very much to be desired. For front-side, just use Google’s search API or something similar.
it will do a basic search, it wont search for usernames.etc for that you prob have to use googles
Is it any good?