I made the request for google adsense and it tells me to insert the google tag in the HTML of my site.
Where do I post it?

 

<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-**********"
     crossorigin="anonymous"></script>

Where does it tell you to place it? In the head, just before the close of body?

Generally you would add adverts in the location you choose with adsense, as shown here

 

https://invisioncommunity.com/4guides/promotion/internal-advertising-r57/