Take a look at the config file (/etc/radicale/config). It’s extensively commented. Although you barely need to change any defaults for regular use.

Just create an htpasswd file (with htpsswd, apache-tools or just an online generator) and edit tow lines und [auth] to read type = htpasswd and htpasswd_filename = <the location and file you created>.

The webinterface to login will be available (by default settings) under localhost:5232.

All you have to do then is change the config so Radicale listens on the server’s IP instead so it’s available in in your network. (Plus the usual stuff of making it available from the outside if you need that like for any other sevice)

And any calendar/contact software will bring a wizard that guides you through the process of sync’ing, usually just asking for an address to reach your server, as well as user and password.