These are a set of PERL modules that are designed to be used with the net-snmp daemon and it's embedded PERL mode.
- log4perl (debian/ubuntu package: liblog-log4perl-perl)
- libsnmp (debian/ubuntu package: libsnmp-perl)
Simply copy the files from lib/site_perl/* to somewhere on your system that is within PERL's @INC search path. Generally speaking, I like to use /usr/local/lib/site_perl (so lib/site_perl/NagSNMP gets installed to /usr/local/lib/site_perl/NagSNMP).
Each individual plugin contains an example usage (i.e. configuration that you add to snmpd.conf) showing how to use it.