Click the Add URL button and a popup will come up.
Type in the URL that you want to hide all ads on (such as www.YOURSITE.com/register)
Trailing slash and http/https don't matter — they'll be stripped anyway.
Repeat adding your URLs for every page you want to disable ads from, then go to your site in the list below and click on the arrow dropdown (to reveal the URLs you just added). Select each one of them and continue to the next page. On the next page I believe you'll select each ad type that should be shown. Uncheck all of them, including the small button at the button about future ad type, then proceed. You can name it.
For example, I have multiple sites that use the same auto ad code. I name mine as such:
Site1.com - no ads
Site2.com - no ads
I don't actually use it on my IPS site, but I set it up for when I want to use it:
But my URLs are customized, except login, lostpassword, and contact. So your mileage will vary. For instance, all of my documents such as terms of service, ad disclosure, and privacy policy are under the /policy page, so including only that one will also remove the ads from /policy/privacy, /policy/terms, etc.
Keep in mind that Google themselves are also very good at not displaying ads on pages they think shouldn't have ads, such as those ones with very little text on them that don't seem like an article.