How I can set which rss feeds are put at my frontpage like that
Feeds are produced by Views.
Right no feed link exists in frontpage. What would be also the right syntax for HTML5?
If you are using node.module (i.e. the /node url) for your front page, that will have a feed automatically. In fact, you can turn this off if you replace the home page listing using Views. See here: http://drupal.org/node/413620#comment-2142182
Feeds will be provided by Views under certain circumstances. Firstly, you have to create a special RSS display for each feed you want to expose. Do this by creating a new view, then adding a display of type RSS and configuring that to expose the information you require. Secondly, for the RSS view to appear on the page you're concerned with, you need to configure the views path correctly. You can configure this to be the front page, if I recall correctly. You can also attach the feed display directly to a page or block display in that same part of the interface.