Where is issue types description and how are they related?

Question

I can't find documentation about how the Jira issues are related (based on their types) and description about them.

As far as I know all the issue types have any kind of relation, for example a feature (epic) can contain some stories, they can be covered by Test Cases, etc.
We are migrating to a new Jira and I can see new features that are not clear at all for me.

Using Jira Server v7.12.3 and SynapseRT.

Thanks.

Nic Brough -Adaptavist- · Accepted Answer

Plain Jira (core) has only two sets of issue types - issues and sub-tasks.  Issues are the heart of Jira, they represent "something that needs some attention".  Sub-tasks are issues in their own right but have one big difference in that they represent part of a bigger issue, so they always have a "parent" that they are in.

Jira Software adds the concept of Epics, which can be linked to other issues to indicate that the stories are part of a bigger story.

That's about it for relationships between issues.  You can also add links between issues, but these are arbitrary and literally just say "this issue is related to that issue because ..."

Jack Brickey · Accepted Answer

I found the following in the Next-gen documentation but it applies to Classic as well.