Confusion on differentiating "Child issue" to a story with "Sub task" issue type

[Deepan V.R]

I have a doubt on differentiating.,

 What do you mean by "Child issue" to a story Vs "Sub tasks" issue type i am creating. Circled by red colour. For your reference..Can you please guide me on this. 

[Nic Brough -Adaptavist-]

This is mostly about Jira-speak, which can be confusing.

• Jira uses the word "issue" to mean "something that needs attention that I will track".
• A sub-task is a lower-level issue that lives beneath another issue.
• You can name issue types and sub-task types whatever works for you.
• A Story is a very common issue type, that is often broken down into sub-tasks.

So, in your question, it looks to me like your "child story" is a type of sub-task.   You may have others, even ones called "sub task"!

[Deepan V.R]

Then it's in Story>Sub tasks>child issue..Whether the order in my understanding is correct..Nic?

[Nic Brough -Adaptavist-]

No.  The hierarchy for plain Jira is <parent><child>.  For Software, you can do <Epic><parent><child>, and Portfolio can add other layers around Epics

When I say <parent> there, those are usually "Stories" (but you could name them anything you want). 

When I say <child>, the default names are "sub task" and "technical task", but again, you can name them whatever you want.