Hello Vanina, 

{{ site.footer_content }} - this output tag displays whatever is entered under Pages > Settings > Footer. You can use a content editor here to add text and images. I added a note for you in your test nation showing you where it is. All this does is wrap whatever you input with <p></p> tags. If you have additional code you want to add for styling, for example, you can simply wrap it around the {{ site.footer_content }} output tag in your layout.html file.

{{ content_for_footer }} - this output tag displays dynamic javascript and other pieces of code needed by NationBuilder, depending on the page you are viewing. For example, we only load the slider javascript if you are on a page that is requesting its use in order to speed load time.  Although it is not possible for you to edit its contents, you can use liquid filters to remove, replace or append something - though I would not recommend that as most are essential for proper functioning.

If you have additional code you want to load in your layout.html file, you can simply place it above or below the {{ content_for_footer }} output tag, or in your websites header depending on the code. 

Thanks.