Hi can I know how I command my computer to open an app

Answer 1

Double click on the icon.

*edit*
If you mean via a C++ program, read through this:
https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=vs.85).aspx

It'll help educate you on the CreateProcess() function and how you can create a new process (open an app).

Answer 2

double click on the icon