How do you add ads txt?

[Kane]

In order to run ads on your site, your ad network will ask you to add ads txt? How do you add ads txt on your site? On my wordpress site I use a plugin to add ads txt, whereas on my forums, I upload the file to the root directory. I could also upload ads txt directly to the root of my wordpress site but when I started I did not know how to do it, so I looked for a plugin to add ads txt and I have been doing it until now.