The script engine application is self-sufficient and doesn't need to be integrated with OS in any way in order to execute a script. However during the installation some level of integration is achieved:
PATH system environment variable is updated with the location of the script engine.
Thus, the script engine file name in a command-line can be specified without directory part.
Shell extension "Run as script" is installed.
Thus, script can be run with a mouse right-click action.
Shell extension(s) "Open as script" is installed (when appropriate).
Thus, script can be opened in appropriate IDE with a mouse right-click action (see Development tools).