$content is populated based on the page you are on.
so on the main rankings page, the templates loop through table_top_row, table_row
on the details page, $content is comprised of the details template.
most other templates are named logically like join_form, user_cp, search_results etc.
the bulk of the edits will happen in wrapper, that is your where your header, footer and sidebar lives.
more details can be found here, though the docs are not overly developed.
https://visiolist.com/docs/styles-design
hopefully, that gets you on the right track. once you get feel, it’s pretty easy to dial in