Stdvar is to be included into the Shapefiles of any part of the developed system via shape's include mechanism. The definitions in stdvar should be carefully designed and maintained for each supported project. They usually concern variant control for all hardware/operating system platforms to be supported or variant settings to produce different qualities of generated code (debug or optimized).
Enclosed in the shapeTools distribution, you find the stdvar file used in the development of the shape toolkit itself. This may be a good starting point for developing an own variant raster. At least, it helps you learning the definition syntax. Otherwise, for a description on the syntax of variant definition parts see the shape(1) manual.