a) make sure, that you have libnet installed. If not,
you can get the sources from http://www.packetfactory.net/libnet,
or, if running under Free/OpenBSD, in ports collection (net/libnet).

b) run ./configure, make, and make install as usual.

c) start program without any keys to run with default setings,
or use next keys:

Usage: cdpd [-i interface] [-d] [-t period] [-h] [-o]
	-d - increase debug level and do not daemonise
	-i interface - interface to send cdp packets on (only ethernet interfaces supported now)
	-t period - period before packets (60 sec by default)
	-h - get this help message
	-o - run once - send only one packet and exit

to modify settings.