Problem with adding header and menus to a page

In HispanicLA.com I noticed that the pages appear without header, without menus and without sidebars. Instead, the content takes all the width. I ignore the reason. So I started to edit one of the pages with tagdiv Composer. Added header and menus. Saved. But eve though now the header and menus appear, but the content of the page dissappeared!
Example:
https://hispanicla.com/esto-es-hispanicla
I tried again with another page. Same problem. I retrace my steps, eliminating the header and menus I have added before. No solution:
https://hispanicla.com/desde-los-angeles-3
The other pages still show the content, without header or menus or sidebars.
I want to add the “pages” menu also to the posts, but I am afraid it will cause the same problem.
Please help, thank you.

Thank you, Ana María. I now understand that there are three areas and yes, I set the header section in “page content”. But a. All the posts also have the header in the page content, and b. I do not see the Header area in the page, so I cannot move the header section to the header area.
Please clarify, thank you,
Gabriel

Thank you, Vlad. I still do not see the header area active, and pointed to the fact that the headers in all the posts are in the content area, not in the header area. What did I miss? Thanks again.