@Ironside, the ads.txt goes on your site at the root level, so www yoursitename com/ads.txt, just like a robots.txt file.
I learned more about it by reading the Adsense ads.txt support page: [
support.google.com...]
Essentially its the media company's name, the pubID#, Direct/Reseller status and, in the case of Adsense, you end with f08c47fec0942fa0. So like:
google.com, pub-ID, DIRECT, f08c47fec0942fa0
This would be the Adsense-related line to cover YOUR OWN Adsense account on your site. There are slight differences when working with other's Adsense accounts on sites you control as well as when working with other ad providers like Media.net but the basic idea remains.
I also studied some ads.txt examples of big sites like this one from BusinessInsider: [
businessinsider.com...]
They obviously work with a lot of advertisers so it looks intimidating but my ads.txt has four lines: my site name at the top, my Adsense publisher info on the second line, Media.net's own Adsense publisher account info on the third line and Media.net's account info on the forth. That's it!