Copy / Paste in various situations

[Y. Makki]

Hello

In my quest to better understand the inner workings of a Linux system,
here it goes. It seems there's 2 independent 'copy/paste' systems, one
which works by a highlight/middle click method, the other by the
ctrl-c/ctrl-v (and the right-click copy/paste menus). Is there any info
regarding this to help clarify how it works? Important question is, is
there a way of combining those 2 systems, so as I could highlight to
copy, then ctrl-v to paste?

Thanks!