In Agility, there are two main areas to manage your content. Layouts, and the Content (area).
When managing content, you may find the content you need to change is in a Layout or it could be linked to a specific item or list in the Content (area).
Layouts are comprised of Component Models that Editors can add to a Layout. Each Component Model can have fields and/or link to content in the Content (area)
This means you can have content fields that are specific to a Layout via a Component Model, or you can have those content fields in the Content (area) and store it outside of the context of any layout.
This separates content into two methodologies:
Keeping your content separate between what will or won't be shared across layouts allows you to stay organized and easier to focus on your most important content.