DAViCal is a server implementing the CalDAV protocol. It's solely a server, with minimal direct user interaction, instead relying on using CalDav clients, such as Apple's iCal.app, Thunderbird with Sunbird, or Evolution.
DAViCal is written in PHP and uses the PostgreSQL database as it's backend to store the calendar information. Currently it only supports PostgreSQL, but there is work to support other databases as well.
# pacman -S postgresql php php-pgsql
DAViCal is a web application, and therefore you need a web server set up as well. For this page, Nginx will be assumed, but DAViCal can run on nearly any web server. (Some may stop processing requests when they see the CalDAV HTTP headers, and therefore DAViCal will not be able to see them.)
DAViCal requires two independent accounts to be set up, one for accessing the database from the web application, which will be limited in power, and another that will be used for administrating the DAViCal related tables.
In order to do so, you will need to edit the pg_hba.conf file, found in /var/lib/postgresql/data/, by default. If the data subdirectory doesn't exist, you need to start PostgreSQL so it will run through the initialization of the data files. (This is done automatically when you first start PostgreSQL via the rc.d script. You can start it and immediately stop the daemon if you want.)