PostmarketOS is an operating system based on Alpine Linux which is designed to run on smartphones, tablets, and other mobile devices. It can at least boot on over 200 devices, and it supports a number of different user interfaces.
The PinePhone postmarketOS Community Edition is one of the first smartphones that actually ships with the operating system pre-installed, and it comes with a version of the OS featuring the Phosh user interface.
When you first boot the phone you’ll go through a short setup process and before you’re greeted with a pretty barebones operating system featuring a notification area, app drawer, and only a handful of applications. There’s a software center, but as of early October 2020 it’s mostly used to update packages that are already installed on your device including system files, the Firefox web browser, and a few other apps.
Installing third-party applications is pretty easy… but it’s also pretty geeky. You’ll need to use a command line.
PostmarketOS uses the Alpine Linux Package Manager, which means that you can install, delete, update, repair, upgrade, or search for apps using apk commands. Note that this is not the same thing as APK files for Android devices. You cannot install Android apps on a device running postmarketOS unless you first install a tool like Anbox that allows an Android system to run within a Linux environment.
In order to install an application, you would open a terminal window and type:
sudo apk add <package name>
For example, if you want to install the Megapixels camera app (which you probably do if you’re using a PinePhone, because it’s by far the best camera app available), you would type:
sudo apk add megapixels
Note that the first time you do this after opening a terminal window, you’ll be asked to enter your password, which should be the same as the PIN code you use to unlock your device.
Then the phone will automatically find, download, and install the latest stable version of the application from the appropriate repository. You can either launch it from the terminal by just typing the word “megapixels” and hitting enter, or find it in the app drawer.