Where is the best explantions how the "outliner" functions?

First of all for those who have followed and helped me through my
big model periple
A GRAND THANK YOU for all your help
I had a huge brake through since someone called my attention to
the “outliner” that I simply had deactivated long time ago as it seemed
to slow down my process
Since changing that I have managed to catch most of my
escaped pixels that for sure made my model even more huge that it is
and it has now facilitated to proceed
and actually load well into Lumion etc

I know this might come across like stupid
Just wondering how the outliner works?
Is it like a window file manager?
What the difference between the four little dots
the blue line etc
Can I move files to assign them to the right groups etc

Thank you so very much

PS and what is it when I get some of my postings back with like
red highlights in the title etc?

SketchUp - YouTube - search?query=outliner

Thank you very much!