Understanding require and ns macro

In a REPL di
(require '[clojure.set :refer :as set])
(set union #{:a} #{:a :b :c})

' means "don't evaluate this form"
so symbols are used as is and are not resolved, and function calls are just lists
it prevents an error as clojure.set isn't bound
it's the symbolic name of something you want to load
you'd get a syntax error if you used it unquoted

The ' is not needed when used in ns as this is a macro
(ns my-namespace
(:require [clojure.set :refer :set]))

As the ns form is a macro it doesn't try to evaluate the symbols in the require form. A macro can decide whether something should be evaluated
(elaborate)

When calling a function (eg. require) the arguments are evaluated first, then passed to the function

when you call a macro (eg. ns) the args are passed as a list of symbols and input literals and the macro decides what to do with them

I mean a macro usually does evaluate things (clojure macros can use the entire clojure language as needed), but they usually just turn one list (form) into another then return it to be compiled

Start with the REPL examples in the issue, especially the require call and ns form, and compare their explanation with the existing project documentation. Done means the distinction between quoting, function argument evaluation, and macro expansion is documented accurately, but the issue does not identify a target file or test.