Sonata PageBundle usage

I have trouble understanding how 开发者_开发百科to use the Sonata PageBundle, more exactly how / where to add blocks to a page so that content could be customized.

So far, when trying to add a block from the administration site, I got the "message_create_block_not_available" error as also described here.

What would be the correct way to add custom content to a page so that it can be manipulated with the PageBundle?