How do RAM upgrades work?

Not really no.

RAM does not affect game performance, other than maybe a small boost to loading (though an SSD would have a much bigger effect on loading). It has no effect on FPS whatsoever.

RAM is needed to allow an application such as a game to load everything it needs to into memory. A game won't use more memory than it needs (not counting poorly coded games with memory leaks) so if a game NEVER uses more than 6GB then even with 16GB available it still won't. All adding more RAM would do is allow you to have other applications running and loaded into memory at the same time.

A better CPU and/or graphics card are the major components that affect game performance.

depends on the game, with higher RAM you can run it on high FPS, but at some point it might have no effect ( over 16 RAM)

yes

if your computer NEVER uses 6GB and you increase it to 16 you will get no performance boost...