How to add a widget to my site?

Howdy all!

I was given instructions from a third party to add a script (using <script>) above the body html tag.  The best I've been able to do is create a new page, add a code block, and paste the code they've given me there. 

I've also been told an admin from a third party must whitelist the domain for the widget to work, which I haven't done quite yet. I first wanted to check that I'm manipulating code in the right section first.

Any other context or info, let me know, and I can add it to the post.

Thanks!

Above body tag, you can add to Code Block (your way is correct) or you can also add it to Settings > Advanced > Code Injection > Footer