I want to use plugins from nagiosexchange.com but I do not know how to install.
I am using Nagios 3 on a Ubuntu platform.
Please Help I have searched every where an looked at 3 different book but I still cannot find out how to do it.
Well, it depends 
Sometimes it’s just a perl script, in which case copy it to your libexec directory and change the permissions/ownership to make it look like the others (like chmod 775 and chown nagios:nagios as appropriate…). Other times it might be a tarball which might contain an installation routine… in which case you need to download it, extract it (think of it like unzipping a zipfile… "tar -zxf " usually does the trick) and usually there will be a README text file within the ‘unzipped’ directory detailing how to install with something like “perl Makefile.pl” & “make install” which you should follow… more details of what plugin you require installed might help provide a more definitive answer 
Thankyou Very much!!! :o