How are server components called?

[nveid]

I'm digging around trying to find out exactly how the server module/plugins components are called. So anyone that has some expertise in the manner please lend me a hand, how exactly per-say does a particular code piece call a specific plugin in the server code?

I'll give a specific example for one spot I'm looking at.. from shell_user_edit.php, where is the actual call it sends to to ADD users? I can modify how its adding, but to better understand I'd like to know what exact piece of code tells its to call method insert in the class shelluser_base_plugin


Thank you, for who can point me in the right direction.