Hi! I use radicale!

I use it on android. For me, I have to use an app called "DAVx5." That app adds the calendar/contacts from my caldav server (radicale) to my phone. Then in my calendar/contacts apps I checkbox the appropriate calendar/contact list. It looks like you're on android... does this info help?

Radicale doesn't really have a GUI, all it has is a webpage that you can log in to. On that page you can download or upload your calendar/contacts in one file, but that's about it. The handling of everything is done by external apps.

You forget about that UI. Only used to create users. Then use. Cardiac/cal app like Dav5X on Android or similar to connect and do all the stuff like create, import etc

See my wiki at https://wiki.gardiol.org/7-services/radicale

It also shows how to install infCloud to get an actual web GUI to use calendars from your server

Yes, radicale works great, but the UI is pretty spartan. It will manage the data, but requires a client to make edits or view the content.

First, you will have to export any existing calendar and contacts as files. It depends on what you're currently using. Contacts should probably be a vcf file, and a calendar should probably be an ics.

Next, use the ↑ button in radicale, select the exported files, and it will create a new "collection" as shown in your post. You can also create a new empty collection to use as you wish. Radicale will not merge files, but you can use a client to do that once you have created the collection in radicale.

You will have to find a client that will sync. On Android, DAVx5 will integrate it into the system so basically any client can access it. Certain Android apps may connect directly, but it's pretty hit or miss. On desktop, I use Thunderbird which works very well, but there are other options. You will use the blacked-out URL in your post to add the contacts and calendar. Check the individual app documentation or make another post if you want help.

Oh, and the last thing... Of course the client will have to be on the same network. If you want to access it remotely, you will want to set up something like wireguard (I use Tailscale, which is dead simple).

FYI, you can just edit your post, you don't need to delete and post again

Unfortunately I don't use radicale so I can't help much on that front

Radicals is an amazing software but I also struggled to understand the concept at first, the documentation assumes you know so much already, which you normally don't. But once you get through the initial hurdle it's really reliable and uses minimal resources.

There are many different clients available

What is the use case?