Configuring WiFi for Screenly Pro is much like configuring a device with a Static IP.
The easiest way to do this is to use the Screenly Configuration Wizard.
Once you have generated the configuration file, save it to the boot partition of your SD card. On a Windows or macOS computer, the boot partition is the only partition that will show up when you insert the SD card into your computer.
Alternatively, you can create a file called network.ini in the boot partition, (or you can just copy the existing sample file). If, assuming you are looking to use DHCP, you would add the following lines to the file:
(Note that there is no passphrase specified)