How to access CLI

A newbie... a super easy... how do I access the CLI interface? Help didn't help to the obvious...
another ... an easy way to insert a file up in the hierarchy, not inmediately below.

Do you want to run Opus commands directly? Or from outside of Opus? Or do you just want to edit toolbar buttons or hotkeys which can run commands? Or something else?

You can do them all, but the instructions are different for each one.