Template Content Area
The Template Content Area makes one region of a template editable in Oxygen on every item
the template applies to.
The template holds the frame — a header strip, a sidebar, a footer. Where you put the
Template Content Area, each item gets its own area: open that post or page in the builder
and you design what goes there, while the frame around it stays in the template.

Change the frame once, in the template, and every item updates. What's inside the area
belongs to whoever edits that item.
Adding one
It's in the Dynamic category of the
Add panel, and only appears while
you're editing a template. Put it where the per-item area belongs and build the frame
around it.
A template can only contain one. Try to add a second and Oxygen refuses with "You
can't add more than one Template Content Area."

On the front end
The template renders, and the item's own content is rendered inside the Template
Content Area, between its opening and closing tags. Everything else in the template
surrounds it.