For the latest documentation on getting lists of groups, and events, for a place, category, or whatever else see the notes on the wiki.
Administrators of groups can 'Create new Event ical importer in group', link in the grey section where others can add events. You just need to fill the iCalendar feed into the 'FEED URL' box. If your events do not have geolocation you will also want to select the default 'Offline' location for events.
Each group has an link to it's upcoming events feed on the group page.
Link presently missing, the URL will be https://radar.squat.net/ical/node/XXXX where XXXX is the group ID (see notes in API above).
Feeds of the other upcoming events pages to be created.
All pages are marked up using RDFa primarily (but not only) using schema.org. You can see examples of the data by looking at the output of the Google (yer I don't know of a better example) Structure Data Testing tool https://search.google.com/structured-data/testing-tool#url=https%3A%2F%2Fradar.squat.net