JIra Greenhopper - how to do Agile correctly

Question

I am new to the Agile flow in JIRA + Greenhopper. I am trying to understand what is the correct/better way to work Agile in JIRA + GH. I've read on the net for some information - so far, I understand we have Stories and Epics (which are LARGE stories). I wanted to know what is the flow of creating the tasks:

1. First, we open a story/Epic and define it in a non-technical text.
2. We can create subtasks to the story ( I have technical-subtasks only now).
3. after opening the story - For development, new tickets (bug/new feature/task etc) are created and are linked using the ISSUE LINKING to the story.

Is this the correct flow? My questions are:

1. I dont understand why in (2) we should open subtasks for technical issues if I open development tickets seperately and link them together - so what is the purpose of the sub-tasks in story?
2. Is there a better/easy way to create the dev tickets directly from GH? or must I open them seperately and link them to the story parent issue?

Thank you very much for the quick response.