Normally the sidebars are used for secondary menus, lists, polls, forms, etc.  Each of these is called a "block" and these blocks are managed a bit differently from typical pages.

When a customer has many pages that have an accompaning sidebar block it becomes a little cumbersome to create a new block for each page.  Therefore a custom block is used that knows what content should go with a page.  This way a single block can do the work of many.  However only the site admin who knows PHP should configure the block.

Since the custom block is written in PHP code there has to be an easy way for clients to find and edit the content.  This is accomplished by putting an [edit] link above the sidebar block when the client is logged in.

The link is a shortcut to the block's content page where the page is edited like any other.

Link on custom sidebar content