the path specifies the synthesis server which is run as a unix command when pressing the boot button of the main window. it must point to the file scsynth[.exe]
in your supercollider folder! the path is usually something like "/usr/bin/scsynth"
or "/Applications/SuperCollider_f/scsynth"
.
note that traditional computers are not shipped with supercollider pre-installed, so you may have to install supercollider first before using eisenkraut. the main supercollider site is supercollider.sf.net, which has download links for all platforms.
the recommended version is SuperCollider 3.2 or newer although it should work with older SC3 versions.