I’m trying to use Nextcloud. I got through step 1, downloading and then unzipping the .zip file. I got to step 2, downloading the Mac client (.pkg file). When I open the client, it asks for a server address. How do I obtain this address?
It can work at for some webhosting companies, but it depends a bit on their setup and the overall performance in generally very limited. A VPS is much better. Of if you want to test, you can try the raspberry pi (not the best performance but a nice thing to start with, there are ready to go images, e.g. the NextcloudPi: https://ownyourbits.com/2017/02/13/nextcloud-ready-raspberry-pi-image/).
So it’s required to use a web server? I was under the impression that anyone could host their own server.
That’s right, but if you want to connet via network or internet, you need a little bit of infrastructure for handling the net communication (Linux and Web server) and a persistance instance (database or filesystem) to save data centralized. And nextcloud server is written in PHP. Because of this, you need an PHP interpretor. All of the above is something you find on every hosted server.