CalDAV is for for calendar sync, CardDAV is for contact sync. Both are based on the WebDAV protocol.
Got to https://account.milliways.info to activate the Radicale service.
You can use your main password or multiple token like passwords for different devices.
You can use a browser to edit your calendars / adressbooks. Open https://calendar.milliways.info for that.
There are different clients out there, here a tested list.
Go to https://calendar.milliways.info/ for administrate your account.
to get a very simple web client.
Here I can recommend DAVx⁵.
Use "Login with URL and user name". URL is "https://calendar.milliways.info"
Thunderbird + Lighning.
Get the CalDAV/CardDAV urls from the webinterface.