[dev] Implement the HelloWorld module

Hello Community, I'm new with OTRS but I find it great. I was trying to setup my first module but I have some problems. It is not clear to me if I have to create new directories for the developed modules or I can use the dir already present. Can someone give me a first help? Moreover I tried to create the files in already existing directories and I was successfully to have the new module in my control board but I have this error code: Software error: Can't call method "FatalError" on an undefined value at ../..//Kernel/Modules/AgentHelloWorld.pm line 29. For help, please send mail to the webmaster (webmaster@localhost), giving this error message and the time and date of the error. Thanks for support, Valerio