Power App was brought into the market to reduce the developing time taken by the developers. With this app you don't need the prior knowledge of Power App, you can customise your own power app and share it like a document. Apps built with Power App is compatible with almost every platform (Windows, ios, android, tab, web).
As of now, signing up with a personal email like Gmail and then creating an app might not be successful as they delete it without prior notice. You will have to use the business id to create the app.
You can check out this link which gives a detailed step of how to build your own power app.
Maybe other knowledgeable members can respond to "What are the elements of Power apps and how it's different from Mobile Apps."