I'll try to give some quick answers so you can spend some time playing with and exploring NVDA yourself, which is really the best way to eventually get the hang of it.
I will presume that you are using the desktop keyboard format, meaning that INSERT is what will be your NVDA key, and this is the default layout. If you happen to be using the laptop layout, which is not the default, even on laptops since most have number pads these days, then NVDA would be CAPS LOCK. Some commands change slightly depending on the keyboard layout you are using, but I'm going to presume the desktop layout.
NVDA has multiple help files, all of which can be accessed via the NVDA Main Menu, Help Option. That would be NVDA+N,H. The "two biggies" are at the top of the list that's the User Guide, and Commands Quick Reference. I cannot tell you how often I end up hitting NVDA+N,H,Q to bring up the Commands Quick Reference in my web browser to find one of the commands I don't use often.
NVDA also has an Input Help Mode, that can be toggled on/off by using NVDA+Number Row 1. When it's on, pressing any key or key combination will cause NVDA to report what that would do, but not do it. You have to toggle it off again to go back to normal mode.
Say all, which is what I think you mean by read screen, is NVDA+Down Arrow.
Reporting the status bar, if there is one, is NVDA+End
Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363
Power is being told you're not loved and not being destroyed by it.