Cert creation related

Help
1

If someone is starting out testing CA signed certs in their QA environment, are there any basic pointers to get started which includes how would one create their own domain names in test env.
I have already looked at Docker based command and many others which are really not Getting Started.

Also, Is it possible to create a cert chain with multiple intermediate certs?

2

A proper chain should include all the necessary intermediates.
So yes.
But if you are thinking to introduce your own intermediate, that won't be possible; the chain must be linked and there is no way to link any additional intermediates into that chain.