Re: How do I access "system tray"?
Richard Turner is absolutely correct that WinKey+B throws focus to the system tray, known officially as the notification area. You'll land on the notification chevron first, which if activated will cause the notification overflow area to pop up showing the icons you don't keep on constant display in the notification area.
Just because it's handy to have: Windows Keyboard Shortcuts
That page defaults to those for Windows 10 when opened, but there is a dropdown at the top of the page that allows you to get them for Windows 8.1 or Windows 7 as well.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore