theses are methods defined by UPnP standard. Have a look at http://upnp.org/specs/gw/UPnP-gw-WANIPConnection-v2-Service.pdf for UPNP_AddPortMapping.
To see more specificaly how to use with libminiupnpc, see the upnpc.c sample program. https://github.com/miniupnp/miniupnp/blob/master/miniupnpc/upnpc.c