I need to use to suggest me a site with information on the German concentation camps and the holocaust (vey easily explained).

It is designed for English learners at an intermediate level.

Try these sites.

http://history1900s.about.com/od/holocaust/tp/holocaust.htm

http://www.pocanticohills.org/amprogress/holocaust.htm

This site may be useful because it's presented in several languages.

http://www.ushmm.org/wlc/en/article.php?ModuleId=10005143