Correct me if wrong.
1. Current focus is where your screen stop at. Example, a field you click, that is your current focus, you may paste text into it.
2. View ID is hidden field which is only seen by app but it's powerful option to choose on some actions like text clicking, field selection. Example, you ay Search Text action to find a text "Testing" & obtain its ViewID (index:xx) & apply click action on it, ViewID may permanent or non-permanent depends on the screen that you view. Example, I'm using ViewID to click on scroll to bottom action in Whatsapp because it has permanent viewID (com.whatsapp.id/scroll_bottom).