The F-Droid app supports adding more repositories (think like apt/yum/dnf on Linux) easily, so you can source software from anywhere which runs their own repository. One of the most popular "other" repos is Izzy (apt.izzysoft.de/fdroid), and there is an alternate project called "microG" which can allow you to use Google Play store apps (microg.org/fdroid.html). microG is how you will get your Google Play apps onto the device, usually (there are other solutions besides microG out there however).
The CalyxOS install ROM includes F-Droid (app and repos) and offers to install microG for you on your first boot (as well as some other opt-in stuff). Calyx runs their own F-Droid repo which is pre-added to the app so you get updates from them as well (think the built-in apps most smartphones have).