Maybe I haven't found it, but I still struggle with the symbols and output. I can usually muddle through, but I would be happy to sit down with a complete, thorough explanation of all the symbols, etc. I only seem to find piecemeal answers and never exactly what I'm looking to understand.
I can top sunbathing: https://wiki.gentoo.org/wiki/Full_manpages/emerge appears to be the emerge manual page, hosted on the Wiki. On principle, I recommend using the local documentation though, since what you find online may be for a different version of the tool than you have installed.
If you using KDE Plasma, and love it more formatted - then try man:emerge in krunner (Alt+Space) ,
this shows the emerge man page in your default browser:)
Edit: I think it is from kde-apps/kio-extras[man]
+ + man : Enable manpages KIO worker