Use Build Main File to compile and link all of the
  changed modules of a multi-module program. The Build
  Main File command compiles and links all out-of-date
  files, except missing .QPU files, and creates a single
  executable file. A file is out of date if it has been
  edited since it was last compiled, or if it has been
  compiled since the main file was last built. The main
  file is always recompiled.
 
  Use the Go command in the Run menu to run the program
  after it is built.