Content-dependent sidebar menu

Hello.

This is a not difficult question, I guess, but I would like to ask it in order to learn.

When showing a page (static content) within a given category, I would like to show also two “basic” sidebar menus:

(1) One menu listing the documents or sub-categories that are down on the document tree (I mean, the list of the sub-categories that have the current category as their parent).

(2) One menu listing the rest of documents belonging to the same category.

How can I do that using templates, I mean, what code should I insert into my template?

Sorry for my English and my poor knowledge about templaltes.

Thank you in advance.