Hi Asamr
To answer both your questions: The editor is the part of PAD where you build your workflows (also known as the flow designer). As opposed to the console, where you have an overview of your processes and settings for PAD. It's also worth noting the distinction to Power Automate, the online workflow engine, which resides in the cloud and allows you to use default connectors (integrations) to a lot of applications.
I would recommend that you go through these two short introductions, to familiarize yourself with some of the terms:
Get started with Power Automate
Get started with Power Automate Desktop
RegEx is an individual discipline within programming, which allows you to search for patterns instead of specific text - i would recommend reading about it, and for quick use, perhaps reference a cheat sheet like this.