I created a basicmodule and now I want to know how to develop that module to do a specific task using my own code. Actually I cannot understand about the structure of the module and how we write a new code to that module. any help would be much appreciated
I hope you already followed the initial documentation to create a module. Actually, modules will be integrated on top of OpenMRS Core and you can extend those basic methods from your methods. So what type of task would you like to perform through your newly created module?
 - https://wiki.openmrs.org/display/docs/Creating+Modules
As a simple task, If I want to print a hello world on screen how to do that ? I mean I know how to print hello world using java but I want to know how to do that in this module ??
Can you please take a look at OpenMRS technical overview documentation and get some understand the OpenMRS technical background. https://wiki.openmrs.org/display/docs/Technical+Overview
Just printing the hello world in Java is very simple since that was a standalone application. But OpenMRS modules are connected with Core and need to attach with that to start working. Simply you can define a variable for your JSP view and return the “hello world” from your controller will work for your request . I hope, following guides will help you to overcome from here,