The NSCL Scaler display is described in the Scaler Display Software chapter and associated reference pages. The NSCL Scaler display runs inside a Tcl server to isolate it from the data acquisition data flow. sclclient is the NSCL DAQ aware program that connects to the scaler display Tcl server to update the variables and call the procedures that drive that user interface.
Unless you have a Tcl server or other server program that has a need for a similar set of functions as the Tcl server, you won't need to manually start the sclclient application as the Scaler Display program starts its own client.
The sclclient reference pages completely describe this program, and the various ways it can be started.