when I started
using Unix, the IT group gave me the 8 volumes of the reference guide (man pages in hard copy

)
No user friendly GUI.
Plain old ASCII on a 'Glass Teletype' (ADM-3 or VT52)
I have stacks of manuals that allow me to write syntactically correct commands

that I haven't a clue as to
why or
where in the code, I would ever use them (and never have in thousands of lines of coding in the database program they applied to).
Fortunately, most of Calibre and Sigil settings have help and pertain to the the preference area they are located in.
You are expected to have a basic understanding of book composition (how else would you know what needs to be changed).
There is no magic to getting a nice e-book (don't hit me Hitch

) ,
There is an Craft and
Art to clean presentation.
The best tools in the world do little good, if you have neither Art nor Knowledge in their use.
IMHO, the only truly arcane user portion of Calibre is the
Advanced template language (which only a few need/want to use).