There are lots of stuff in Elisp function prototype. Let's use 
call-process
 as our example.
call-process
create an synchronous subprocess. The function will wait until its process finish.

call-process program &optional infile    destination      display   &rest   args
               ↑     |              |        ↑                ↑     |          | 
              "ls"         ↑                 |               |         ↑  
                     optional argument        |               |        list of arguments
                           ↑                                 |       "a" "b"  ⟹   ("a" "b")
                          nil           '(:file "/tmp/o")     |
                           ↑                   ↑              | 
                         stand input      buffer name        nil  
                                            "foo"

&optional infile => Optional argument like C/C++
&rest args       => It is like argument list in C | "a" "b" => ("a" "b") is passed to function

// SEE: ~/.emacs.d/init.el
(call-process "ls" nil '(:file "/tmp/o") nil "-lah")