Hi Islam,
most of the admin stuff is in the administrators help file in your notes client. If you need that as PDF you can use the free PDFMaker to print it (which might not make sense). You also might find interesting material in the IBM redbooks:
http://publib-b.boulder.ibm.com/portals/Lotus
or the documentation library:
http://www-10.lotus.com/ldd/doc
Hth
:-) stw