Developer API is the same as for Kohana_View. Please refer to public methods of Kohana_View library
If anything goes wrong please refer to source code, I've tried to document it out.
Also I've created a basic Controller_Template that uses Template library to generate a page.
Indicate the block
if (!Template::output($title)): echo "default content here if you didn't redefined the block in descendant template"; endif;
Set the parent of the template
Redefine the block
Template::begin($title); echo "redefined content here"; Template::end();