Suppose the uri of that executable is known:
Will it be executed if we just type it in the address bar?
The answer is "it depends." If your executable is within the web root and has been configured to run as a CGI and has the correct permissions set, then yes, it will run.
If you just have some random file located within your web space, chances are it will just prompt for download. Your web server will treat it as it would any other blob of data on disk.
More specifically, what are you trying to accomplish? Perhaps the answer can be narrowed a bit depending on what you actually want to do.
No, that'll just serve the file for you to download.
You need to use a shell to execute the file, or some server side scripting. For example, in Perl/PHP: