How to organize templates in Bitrix?

Question

1C-Bitrix

Hello Bitrix Guru. Just started studying it. Here there is a header.php, there is a footer.php, there is content between them. Let's say that in this content area there is also a side menu that cannot be attributed to either the footer or the header. How to make it appear automatically in the content part?
Those. in fact, you need a layout nested in the main layout, as I understand it.

Answer 1

Read about the included areas, this is just what you need.

Answer 2

Here it is written.
When you "climb" into the admin panel, look next to it.

Answer 3

You need to do this with the included area. Although it must be defined somewhere. If the side menu does not apply to either the footer or the header, then place it anywhere.