OpenSLP is an open-source implementation of the IETF Service Location Protocol Version 2.0 standard, which is documented in IETF Request-For-Comments (RFC) 2608.
In addition to implementing the SLP v2 protocol, the interface provided by OpenSLP source code is an implementation of another IETF standard for programmatically accessing SLP functionality, documented in RFC 2614.
To fully understand the workings of SLP, it is worth reading these documents and internalizing them. They are not necessarily light reading, but they are essential to the proper configuration of SLP on an intranet.
For more information on the OpenSLP project, see the OpenSLP Web site and the SourceForge Web site. The OpenSLP Web site provides several documents that contain valuable configuration tips. Many of these are incomplete at the time of this writing.