=string= leads to the text being transcribed verbatim. A good hint is to recall that the equals sign kinda implies verbatim.
You can make words *bold*, /italic/, _underlined_, =code= and ~verbatim~, and, if you must, +strike-through+.
The official manual states equals is used for =verbatim= quotes: https://orgmode.org/manual/Emphasis-and-Monospace.html