Coding for a newsletter subscribe pop-up

I've created a newsletter sign up pop up to appear on my home page. I created it a Mailerlite. They provide me with a snippet of code, and gave me these instructions to make it work:

"Install the following snippet of Javascript on every page of your website right before the closing </head> tag."

Do I use code injection for this? Only on page which will have the pop up?

Completely new to coding here.

Hi,

Add it to Home > Settings > Advanced > Code Injection > Header