Emacs help shown using C-h k S-<right> states only:
<right> (translated from S-<right>) runs the command right-char (foundin global-map), which is an interactive byte-compiled Lisp function in‘bindings.el’.It is bound to <right>.It doesn't also say how it comes that S-<right> not only moves the cursor one position to the right (or to beginning of next line if at end of a line) but also results in starting, extending or shrinking a highlighted selection.
This raises the question: Which commands/functions/processes are executed on keyboard input S-<right> along with command right-char?