Usage:

just install the module and adjust the values in config.php to your needs (see the comments in that file for explanations) the file is shipped as config.default.php to avoid overwriting your adjustments during module upgrade.

Your rss feeds are available at the url WB_URL/modules/rss_feed_all/view.php

More advanced hint:
You can also call RssFeedAll_Render() for instance in a code2 section on a hidden page with a blank template assigned. When using it this way, make sure that you suppress the section anchor, e.g. using an output filter.