[Closed] l can not understand the first step:add PHP code responsible for rendering the language switcher on ...

Background of the issue:
I am developing a site and want to float the language switcher using WPML. The documentation I am following is https://wpml.org/documentation/getting-started-guide/language-setup/language-switcher-options/custom-language-switcher/. The first step in the document is to add PHP code responsible for rendering the language switcher on the page.

Symptoms:
I do not understand where to add the PHP code for the language switcher.

Questions:
Where should I add the PHP code to render the language switcher?