DCBase

How am i use this plugin http://sourceforge.net/projects/dcplusp ... t/download ?
Is there any documentation available to develop further plugins in DC++?

The current release version of DC++ cannot load that plugin at all, which raises the question why is it on SF already.

http://builds.dcbase.org/ - has versions capable of loading it, however, they are technically development builds. As for plugin documentation, right now that is still in infancy stages, some automatically generated documentation exists on the launchpad pages for plugins https://launchpad.net/dcpp-plugin-sdk-cpp and https://launchpad.net/dcpp-plugin-sdk-c.

Currently the best way to learn how to develop plugins is to dive head first into it and certainly look at the plugins that already exists, two of them are very much intended as examples (TestPlugin and ExamplePlugin respectively), but the others also provide good examples as to what kind of things and how certain things can be achieved from a plugin.

The launchpad projects linked also include skeleton plugins for easy start.